Oh, and yes somebody mentioned the 8600s with the slow ram: If it's got DDR2 it'll be worse than the 7600GT. The other models with DDR3 are noticably faster, but end up probably being marginally faster than the 7600GT. Basically I'd avoid the 8000-series entirely unless you're going full-blown 8800.
Especially considering the new mid-budget, high-power, 9600GTs out!