You’ll need more than 1gb of GPU ram, battlefield 3 at 1080p a 2xAA uses 1.9gig of ram on my GTX 670 ggb version. Got for 2gig minimum on the GPU.
If just for gaming than the hyperthreading on the I7 chip sets are not really needed, so go with an I5.
8 gig of ram is plenty, 64bit OS, got for a 120-256mb SSD for the OS and game installs, a larger mechanical drive for stroage.
Make sure you get a decent psu, Budget at least £80 for this and stick to a good brand (Corsair ect)
You building or buying?