Yeah, the X800XL is easily the more powerful card. But if SC:Double Agent is on his play list, he would need an SM3.0 card. A 7600GS would be a step down in performance though, unless he gets a GDDR3 version and OC's it.
I totally agree. Besides, the 7600GS is not really powerful enough to fully utilize sm3.0. IMO anything less than a 7600GT isn't worth getting just for sm3.0.