The generations are too far apart for any common game benchmark with the exception of Crysis. Look for a benchmark for each of those cards, then adjust the benchmarks for the X1900XTX up a little bit to take into consideration the difference in the CPU since Crysis can be bottlenecked by both CPU and GPU.
As much as people hated it, the 2900XT was faster then even the x1950XT. 2900pro might be around the x1900xt? Which I think was around the speed of the 3850? 4650 or maybe 4670 performance? In terms of which 6 series card I'm guessing a 6670 maybe? Might even be the 6570. Tons faster though I'm sure you knew that.