If you can, Upgrade your processor first.
The way that the Graphics Engine for FS2002/04 works, Most of the load is put on the CPU. The graphic card will help with all the different texturing and visual effects. But of all the information that is processed to run FS2002/04 only 60% of that information is visual (i.e. Seen on the screen) The other 40% is Aircraft flight dynamics, terrain modeling, flight physics, AI
aircraft, ATC, and other things.
With a game like Unreal 2, only 15% is not visual.
So, If you want high frame rates for 2004, spend less money on the Graphics Card and and save for a faster Processer. If you play lots of diffrent games like Unreal2 or games like that, Then put all the cash into a high end Grfx Card.
When you buy your card. If you see a "faster" card with 128 of ram for the same price as a slower card with 256meg, Go for the 128 ram card. Most games can't don't make use of the extra 128 megs even a high texture monster like MSFS:COF