skyrim doesn't need to be ini hacked anymore to take advantage of higher core counts. it used to work, but its defunct now and now any havok/papyrus ini hacks can actually hurt performance. otherwise skyrim wants two cores moving as fast as possible, will use up to six additional cores for random low level crap.
otherwise, the fx6300+r9-280(7950) is plenty of horsepower for 1080p vanilla skyrim, though optimizing and cleaning vanilla skyrim will help, especially for modding. if you dont go too crazy with unnecessary 2k-4k textures, and you mod correctly, you shouldn't have any problems.
but the i3 would be ideal.