Pretty much any new Graphics card will run IL2 easily, what tends to be the deciding factor now is the Processor as IL2 is pretty CPU intensive. I'd go for a faster CPU if IL2 is your main game.
I can't say anything about the Nvidia card as I have not owned one, but I did own a 4870x2 2GB card, and quickly sold it.
Graphically it's a beast and as I have a 1000W CPU, this wasn't an issue. However it runs hot, very hot. At stock speed and just sat in the case running the desktop only, it idled between 83 and 86 degrees Celsius. A little tweaking on the ATi Tuner got the temps. down to between 68 and 70 with a barely noticeable fan noise increase.
However, once you start getting 3D graphics running, be prepared to sit next to a Hair Dryer as the fan goes into overload keeping the card cooled down! For me, noise is a consideration and I just couldn't bare the sound it produced. I now have a Sapphire 4870 2Gb Vapor-X:
http://www1.sapphiretech.com/us/product ... p?gpid=296
which runs incredibly fast and is way quieter than the 4870x2 and suits everything I need it to do.
Just my thoughts, but if heat and noise are not a problem I like the 4870x2
Cheers, MP.