My suggestion is to wait until late Q1 2010 to purchase your new card. Direct X 11 is something which will give you better performance or better image quality and your DX 10 Nvidia cards will tank performance wise in newer games when they try to emulate Direct X 11 effects.
Since you need all the performance you can get even an enthusiast class DX 11 card based on their new Fermi core (GTS class) which should run you $200-$300 given AMDs strong price competitiveness should be perfect for what you're looking to do.







