Radeon HD 7770

[AcceleratorX]

Based on charts in the below link I think the 7770 is catching up to the 6850 with newer drivers. Have a look:

iXBT Labs - i3DSpeed, April 2012 - Page 2: Performance charts

Though it's still on average 10% slower, each new driver brings it closer. For this reason I'd say a 7770 is a better bet now and may be better than the 6850 in the future.

 

[topgear]

look at the performance rating of HD6850 which even at stock speed can still beat an OCed HD 7770 with 1120/5200 clock speed and the performance of HD7770 improved by 0.5-1.5fps at best ( 1920*1200 resolution ) from 12.1 to 12.4 driver version in DX11 game titles.

iXBT Labs - i3DSpeed, February 2012 - Page 2: Performance charts