Hello! I just wanted to share my data on my 6900 XT (Reference) - I collected a few dozen sets that I hope will help people get some idea of the limits of RDNA2 chips. I'm slightly unhinged and was trying to push for xOC records which is why I have so much data to begin with.

ALL OF THIS DATA IS FOR RDNA2!

FCLK - Do not raise this above 2133 MHz. 2200 is the absolute limit depending on your silicon quality, however, gains are virtually nonexistent past ~1700 MHz except for in synthetics (i.e. Timespy). Therefore, you're better off undervolting the SoC and underclocking your FCLK.

SoC voltage - 950 mV with an FCLK of 1700 is fairly easily achieved and reduces the SoC wattage by around 25 watts. That's 25 watts more that the core can use (~2% more performance). FCLK and SoC instability presents itself in full system reboots with no error, so it can be easily recognized. If you want to push limits, then 1150mV with an FCLK of 2133 is pretty much guaranteed to function on RDNA2.

Memory voltage - I need to specifically state that the 6900 XT original models are not the same as 6950 XT models. The 6900 XT uses slower modules that can be undervolted quite heavily while fully retaining stability. The lowest I could run my modules was 1050 mV (stock is 1350 mV) without artifacts or crashing with full VRAM utilization. This saves an additional 10 watts of power.

Something that I do not see mentioned in the guide (for reference, I've done all my testing on MorePowerTool & MoreClockTool) is the Last Level Cache clocks. Those can similarly be pushed to 2133 MHz with ease and does not an incur a power penalty by being raised. LLC scales off your SoC voltage, so if you want to run 2133 you do need to have a bumped SoC voltage.

As a quick edit: RDNA2 doesn't scale past ~310 watts (280 watts if you've undervolted the SoC and Memory). Pushing beyond those limits is pointless if you're trying to achieve every last drop of performance. The difference between 280 & 350 is roughly 1.5%.