System :Intel Core2Duo E8400 (6MB L2-Cache; 2x3ghz), GeForce GTS 250 or ATI Radeon HD 4850, 4GB DDR2-1066 Ram. (Thermaltake Litepower 450W PSU), Which is the Better Vid Card ? Nvidia or ATI?
The GTS has higher FPS than 4850. There’s an site online that has a benchmark on ten of each vendor and they rated the GTS or GTX the highest over the 4800 series. Though I would go for the 9600/9800 if you are not using SLI/XFire mode. SLI/XFire mode would blow your power supply if you are not using a high enough power supply.

450W would be the minimum power supply requirement but it says on the box “450W minimum or greater power supply” “X Watts for using Crossfire Mode” or “SLI Mode” meaning it can be double if you use the modes on one card or two cards.