Pretty Awesome setup you've mate
,
But to be honest squeezing a new graphic card to reach higher in IL2 won't really help, it's as simple as that the game ain't optimized for new GPU's.
There are graphic issues and there are FPS issues, but it's the game to blame more or less and not the cards.
Btw i am thinking of trying the new 4870X2, should be the best card on the market right now, since ATI released it a couple of weeks ago.