Just look around for like 50 bucks more u can get a quad core and not only make your system a bit better but it future proofs it a bit also. something u seem intrested in doing.
With Nvidia's current offerings I would not even think of picking up a GTX unless I had money to burn. You'll need a good size monitor if you want to use it to its full potential. G92 8800 GTS is the way to go. Consider grabbing a 500gb 7200.11 32mb cache seagate instead of two 250's