I cannot find any FPS tests for the 4850 against an EVGA gts250, which IMO is better than any other brand. They have pretty much the highest stock clocks, and are the most overclockable! I haven't seen anybody get close to my nearly 18k 3dmark06 score running a single 4850 with a Phenom II.
Closest comparison I've found so far, even being intel, was a core 2 duo
[email protected] and an overclocked 4850 (800/1125, stock was 625/993 so thats a large overclock) scored 15,156 with a CPU score of 3581. Now, with my Phenom II 550 as a dual core at 3.8ghz, gts250 OC'd to 825/1350 (stock 756/1100), I score 15,5xx with a CPU score of around 3100. So, I have a lower CPU score with lower CPU clocks yet I score 400 points higher? Thats all simply GPU being better there.