
If you bought a brand new AMD AM5 Motherboard along with an AMD 7800X3D or 7950X3D or the newest 9800X3D, congratulations! You have the best architecture and CPU for gaming in the world right now!
That said, like for all things, the "stock" experience with those Motherboards and CPU configurations can be noticeably improved with faster boot times, increased performance and consistency, all while consuming less power and being more silent.
All of this by tweaking your BIOS so I will try to guide you at best for optimizing it the most :)
DISCLAIMER: Updating and changing BIOS settings will NOT void your warranty but it's still a very delicate process which should be done only in a stable environment (with no power loss) and only if you exactly know what you're doing. If you don't feel confident in doing so, you can stop reading right now.
DISCLAIMER #2: The following optimization guide is based on an ASUS AM5 Motherboard, but you'll find most settings in all other manufacturers' AM5 Motherboards, just in different places. If you don't find specific ones try using the Search function or still go ahead with the others.
1. Update your BIOS to its latest "Stable" version

First of all go to your manufacturer support webpage for your specific AM5 Motherboard, then under their Drivers/Utility/BIOS/Firmware section to find the latest Stable (not Beta) BIOS version to download. Once downloaded, extract it (and rename it using the specific .exe if you have an ASUS board) and put it in an USB drive formatted in FAT32.
Keep the USB drive plugged and turn off the PC.
Turn on the PC and keep pressing the F2 or Del key when you see the BIOS logo to enter the BIOS settings page.

From the Advanced Options / Tool section you can launch the BIOS update utility from which you can select the updated BIOS file in the USB drive and launch the update itself.
IMPORTANT: Be sure to have your current BIOS to its default settings BEFORE launching the update for it to be as smooth/without issues as possibile. If that's not the case, "Load Optimized Defaults" and reboot before launching the update.
Also DO NOT UNPLUG OR TURN OFF THE PC DURING THE ENTIRE UPDATE PROCESS
2. BIOS OPTIMIZATION (in Advanced Mode)

Select an "EXPO Tweaked" or XMP profile (if available) for your RAM: this will load an already tweaked/optimized and more importantly tested profile for your specific RAM with lower latency and faster speed

Starting with BIOS containing AMD AGESA update 1.2.0.2b, there is a new option called "Core tunings Configuration for gaming" (or "Latency Killer" in other BIOS) which I recommend to manually set to Level 1 (or Enabled in other BIOS) in order to noticeably lower memory latency (while staying stable) and therefore improve both 1% Low fps and Average fps in all games (up to +7%), along with much improved input latency

Enable both Power Down Enable and Memory Context Restore: usually under DRAM Timing Controls. It's important that both are enabled at the same time. This will drastically reduce the PC boot times from 20-40 seconds to only 6-10 seconds

Enable Core Performance Boost: this enables the CPU to use it's boost clocks; should be set to "Auto" which should already mean "Enabled", but better be sure and have it Enabled manually

Enable Medium Load Boostit: to make boost clocks both higher and more consistent also for medium load scenarios, for example games in particular

Set Precision Boost Overdrive to Enhancement: this is the latest version of PBO which will squeeze the most the CPU speed under load while respecting a temp limit which can be set below

Set the PBO Enhancement Thermal Limit to Level 1: for best and most consistent PBO performance. Don't worry about that 90°C temp limit, those CPUs will never reach that when setup with all my other settings. So we can move on to know why :)

Set CPU Boost Clock Override to Manual and set a Positive Override of 50: this is a very minor overclock which will ensure PBO to actually reach your maximum boost clock speeds when needed
Set Curve Optimizer to All Cores + Negative 20: this is a very important setting which will basically undervolt your CPU by a very good margin without being unstable for most users, ensuring that boost clock speeds are kept longer and in a more efficient way with cooler temps and quieter compared to stock. If for some reason you will face instability with this (for example Windows crashing entirely when you leave it alone in idle for a while) try lowering the value to 15 and see if it happens again. If yes lower it to 10

Disable "Native ASPM" & "CPU PCIE ASPM Mode Control": to remove energy efficiency states to PCIE to avoid microstutters in-game. The extra power draw with those states disabled is minimal while having constant and full PCIE bandwidth when needed is a much bigger benefit for games.
To be sure ASPM is totally disabled also search for these options and disable them if you have them:
PCI Express Native Power Management: DisabledASPM: Disabled
L1 Substates: Disabled
PEG ASPM: Disabled
DMI/Chipset ASPM: Disabled


Disable unused Controllers: for example you can disable the motherboard USB Audio Controller if you only use the dedicated GPU HDMI Audio or Bluetooth and LAN Controllers if you don't use them but you only use Wi-Fi or vice versa. The more you disable the less power you will use and the faster the PC will boot

Disable Legacy USB Support: if you have modern hardware (AM4/AM5 motherboards) to improve startup time and DPC latency

Manually set Global C-state Control to Enabled: as the default "Auto" setting may actually translate to "Disabled" for some motherboards and/or BIOS version. Manually setting Global C-state to "Enabled" will make sure AMD CPUs efficiency (both in Idle and under Max Load / Max Boost Clock) is preserved instead

[Only for 1 CCD CPUs - like 7800X3D/9800X3D and NOT 7950X3D/9950X3D]
Disable CPPC Preferred Cores: to let Windows treat all cores equally (as they're all P-Cores, equally Performant cores) and better distribute workload between them and guarantee smoother frametimes and less stutters in-game.
If on some motherboards you don't have the "Disabled" option but only one of these:
- Auto
- Driver
- Cache
- Frequency
Leave it to Auto


Disable both Clock Spread Spectrum and VRM Spread Spectrum: to ensure the CPU base clock is perfectly stable without artificial fluctuations introduced by Spread Spectrum (to try avoiding electromagnetic interferences with the nearby devices)
Personally not only I hadn't any issues with nearby devices with those two off, but the overall stability and framerate consistency have improved as well

Disable "Download & Install ARMOURY CRATE app" (for ASUS boards only): as Armoury Crate is borderline malware (resource hog, difficult to uninstall) and it's basically useless as you can do all it does via BIOS, Windows Update and much better applications. This setting change will prevent the PC to auto download/install it
3. Set a Manual/Optimized Fan Curve
After applying all the changes above and "Save and exit", re-enter the BIOS after reboot to set a custom fan curve for your new settings.

Let the PC settle with stock temperatures for 4-5 minutes, so don't touch anything, then enter Advanced Mode/Settings again and in case of ASUS BIOS click on Q-Fan icon and then on Optimize All or Q-Fan icon again located in the position above. The BIOS will automatically test all PC fans for the best curve possible for the settings in use and provide some changes at the end: accept that.
There should be something similar also for other manufacturers' AM5 BIOS.
4. "Save and Exit"...and Enjoy :)
Congratulations! After saving and rebooting into Windows you will now have a faster, more consistent, more responsive experience while also having lower temperatures and a quieter, Optimized experience.
5. Test the PC stability with OCCT (Optional but Recommended)

If you want to be 100% sure your PC is stable after all these tweaks, the best way to do that is by using OCCT (even the Free version is enough)
Just download it from here , put it in a folder (as it's portable, no installation required) and open it. Then:
1. Select the "CPU + RAM" test, leave all its configuration as is (default) and launch the test for 1 hour. If you pass it without errors, you're good! If you have even a single error during the test, you need to tweak down some values as it may be too aggressive for your specific hardware (the main culprit is usually the CPU Undervolt using Curve Optimizer, so if for example you used a Negative Curve at -20 and got errors there, try a less aggressive undervolt of -15 and repeat)
2. After you passed the CPU + RAM test, I also recommend to launch the "3D Adaptive" test changing from default settings the upper % of the GPU test (so from 10% to 100% instead of 60%) and change the increase interval to 5% (from 4%) each 30 seconds. If you also pass this 1 hour test, you're super good :D ! It means your entire PC config will be stable with everything you throw at it so if you still have crashes with some games, it's games' fault (software side) not yours (hardware side). If you instead have even a single error during this test, most probably you also need to use a less aggressive GPU Undervolt (to re-tweak in MSI Afterburner this time, not the BIOS) until you pass this test again.
BONUS:
BIOS versions usually reach a "mature" and actually stable status after around 1 year the release of a Motherboard
Further updating BIOS in the future may reset all your custom settings and you will need to re-enter all of them
If after updating the BIOS and all these tweaks everything is running fast, stable and with cool temps for you, you don't "have to" update your BIOS every time you see an update on your manufacturer site but you can stay with the version you have without issues
If you have crashes in Windows after the changes, the first thing to do is lowering Curve Optimizer Negative value for All Cores to something lower than 20 (so 15, 10, 5 etc.) and/or change the RAM EXPO preset to something else (like EXPO I or II instead of Tweaked) until everything is stable again
Enjoy! :)
-P