I've asked some questions about this..
..and the answer I got from my friends, was that the NVidia GeForce FX5900, is the most cost-efficient to buy and prepare for the next 3~5 years of computer use.
My GeForce4 MX440 is starting to show age, and it can barely keep up with IL2:FB/AEP. I'm thinking to change to the FX5900 too.