Or possibly a GTX 460. Generally though that's a bit overbalanced on the CPU side. You'll get better game performance with a lesser CPU and more GPU, but if you play CPU intensive titles then it might be the way to go.
If you want to keep things playable during epic battles, we recommend at least a 3 GHz dual-core or a 2.8 GHz triple-core processor. We also suggest that you opt for a 3.4 GHz Phenom II or a Core i5-750 at the very least to ensure smooth gameplay at all times.
Basically, if you want my take, for Starcraft II you need a strong processor but a medium level GPU... NOT because that's the best gaming system, it not. It's just that SC II is so hard on GPUs it's best to run everything on medium settings anyway, and medium cards like the 5770 or GTX 460 or 5850 will do all that can be done anyway.
So take my initial build and see if you can fit in GTX 460. If so you can always add a SECOND GPU later, because the PSU can handle that. If not that then the 5770 will work and you can add a second one of those later as well.