okay but then again you can't compare an ATi Radeon 8500 with the latests X1900 series & X1950 series cards, so kinda exagerated imho, and for OpenGL that's abit dead for the gamers market, it's overall Direct3D which is being used as the main API of choice for most games.
but yeah I have heard the rumors but , to believe them is something else, a friend of mine has Redhat 8 and he used an X1800XT 256MB and he has no problems what's so ever, he plays games like Quake3 and 4.
but anyways might depend on what Linux version you are working with I guess, since there are many types.
I rather stick to a microsoft OS as most gamers do lol.

for your side get a sweet GeForce 8800 GTX ala G80 and rock'n roll

I wouldn't mind hav'n one of those myself
http://www.dailytech.com/article.aspx?newsid=4812

Half Life 2: Lost Coast loves the GeForce 8800GTX. Here the GeForce 8800GTX is able to show significant performance gains over AMD’s ATI Radeon X1950 XTX—approximately 92%.
Quake 4 shows similar gains as Half Life 2: Lost Coast too, an approximate 92% improvement.