I'd definitely prefer a 6xx chip over a 5xx one. They are simply engineered much better, so they don't run like furnaces and support Data Execution Prevention and 64-bit. That being said, I'd much rather have either an Athlon 64 or a dual core chip (again, Athlon X2 is preferred but Pentium D is still better than a single core P4 in the long run). After all, for the $400+ that a 650 costs, you could buy one hell of a single core A64 (4000+) or for $100 more you could buy an X2 4200+, which friggin rocks. You could even grab a 3.0GHz Pentium D, probably for under $400. If you don't want to upgrade a lot, then dual core is really the way to go, since in a year you'll definitely regret not having one if you decide to buy a single core now instead. Also, if you like gaming, THEN GET AMD!!!!!!