If this were Slashdot we couldn't even have the discussion without being swamped by fanboys claiming completely false things about Linux gaming. I've been trying over and over again for about 15 years playing all different types of games on different types of hardware and roughly speaking I would say an average of 20-50% performance hit on 3D rendered games but it is getting much MUCH better.
It does work but I didn't spend the, honestly, stupid amount of money on my home PC to have it perform worse than it can just based on the software I choose.
There's a billion reasons why this is the case so saying one specific thing or manufacturer is going to fix it but AMD pushing support is a wonderful thing. I can't wait until I can finally get rid of Windows completely.
Really what I would love is a gaming focused Linux distro that actually works.