Hyperthreading is not really used for gaming atm so the 680 build will more likely have an advantage. if one wanted a better cpu, then theres normally a jump from i5 to sandy/ivybridge-e 6 core rather than 4 core + HT. but the gains are very minimal.
Dude, get the i5 PC. It has a better GPU which is super important for gaming. Anyway, like dudewitbow said, hyper-threading capabilities don't help gaming at all. If it is a computer primarily for gaming, I would almost always suggest the one with the more powerful video card.