UPDATE:

I've got Corectrl up and running with AMD Overclocking functioning on RDNA2 (6800 XT).

From yesterday's limited testing I'm kinda blown away.

The card runs significantly more efficient under Linux so despite setting the same target clock as in Windows being 2700MHz, the cards actual clock when ruining games and not bouncing off of power limit is only 30MHz lower, on Windows it was usually around 60MHz lower.

But the major thing is that when bouncing off of the power limit I've seen the clock drop only by around 100MHz on Linux but on Windows it was usually a massive swing by 200-300MHz.

VRAM OC on Linux seems to be completely broken though, even increasing clock by 1MHz when on desktop will result in massive artifacts and eventual crash.

Voltage control and behaviour on Linux also seems to behave quite a bit differently than on Windows. Needs further testing though.