S!
First of all, IL-2:CoD runs on DirectX 9 or 10 depending on settings. Even conf.ini proofs it if you do not believe what Oleg and Luthier said
So either AMD or nVidia will run this game adequately given the brands provide driver support/profiles for it.
As of CPU it seems 2500K is the best bang for the buck for now. Paying over 100€ more for 2600K with HyperThreading this game does not even use is worthless IMO. Even my modest rig runs CoD very smoothly and I put most of the performance issues to the messed up coding of the game rather than GPU drivers.
So either way..AMD or Intel CPU or AMD/nVidia GPU is matter of preference. But I would go for something built around the Intel 2500K + Z68 chipset..