GPU: GTX 780 is definitely a good choice atm. Also keep in mind that a heavy modded skyrim benefits from a decent amount of vram the most.
CPU: Honestly last year was a pretty bad year for gaming cards. The current Haswell generation is in my opinion not worth the buy for desktop gaming. 2014 looks more promising for both Intel and Amd so far. I would wait. If it has to be now, I'd recommend buying nothing with over 4 cores, as most games dont support the extra cores anyway. My recommendation for the 1150 socket is the i5-4670K and for the 2011 socket Core i7-4820K, which both can (and should) be oc'ed.
MOBO: The difference between pci 3 and 2 is quite subtle (~4 or 5% improvement). True it will have a slightly bigger impact on skyrim specifically, since skyrim only uses direct-x 9, but still i don't know if that alone warrants a buy if you don't intend to crossfire.