What screen resolution? 6600GT starts to drop off in frames ps above 1024x768.
> edit: benchmarks tell me very little
The difference between the cards should be obvious at 1280x1024 and 1600x1200. If you're happy with 1024x768, get the 6600GT, 250gig seagate 7200.8, and spend the leftover cash on games or more RAM.
Definitely get more RAM if you only have 512 MB instead of 1 GB.