Quad core won't be better than dual core at this moment. In fact, if you force the game to run on only one core, you will have less issues (patch 1.02 has improved this somewhat, but unfortunately it is still true.)
You might want to consider a gfx card upgrade. With what you have right now, you are going to have to run the game in pretty low settings. Though between now and the English release, there could be more optimizations done. But I just wanna give you a heads up, since I can't comfortably run the game at all max'ed out settings with my GTX 295, esp. with the "stuttering" bug/issue.