Starcraft 2 and simcity(the new one coming out), the build is: Asrock 960gm gs3 fx amd micro atx motherboard with phenom II 965 x4 corsair vengeance 8gb ddr3 ram, WD Blue 250 GB Desktop Hard Drive: 3.5 Inch, 7200 RPM, SATA III, 16 MB Cache, and I am debating for the XFX 7850 core ed. unless you can tell me something better?
mobo ram, and video card ram are two separate entities and have no restrictions on each other. as for gpus, 160-170 is the bare minimum for the HD7850 1gb models which have great performance for its price. Current promotions as well would give you both tomb raider and Bioshock infinite on release.