Comparing apples with peaches again?
Proprietary driver vs. a free one which is still in development for R600+ on different boards (okay, the choice in boards was limited by HW indeed) with a limited number of tests.
Compare xf86-video-nv with xf86-video-ati with that setup next time.
OT: And still using ext4? Just because it is the default in that over-hyped Ubuntu?