Guru3D have a trio of ATi cards on trial for the benefit of the world, comparing them against each other and also some of NVIDIA's offerings.
Any game at any settings on all cards will perform absolutely perfectly, in fact with a faster processor performance would be even higher as believe it or not, both x850 cards are limited by the Athlon 64 4000+ CPU. It's really silly, but in several cases the VPU (Graphics core) is waiting for the CPU (processor) to finish up its calculations and send them to the graphics card driver. Don't get me wrong, the Athlon 64 4000+ is powerful enough but see it like this, your graphics card is like 80% at work with certain games. So if you own an Athlon 64 3000+, your CPU probably is not powerful enough to feed the x850 with enough data to maximize performance.
[The review]