Depends on the game. On my quad G5, turned all the way up, S.T.U.N. Runner will run at full resolution, but games like Soul Caliber run at a glacial pace if they work at all. On the other hand, I, Robot renders beautifully, presumably because of the lower resolution and simpler mathbox. I mostly play Neo-Geo and classic arcade in it and that is just peachy.

Deus Ex is a 1st person game, though it's much more than an FPS.