I doubt two extra cores will do you much good in that regard. The 4770K is, albeit debatable, one of the best CPUs currently out. Chances are if the 4770K is struggling with what is essentially four GPUs, there's not much else out there that will handle them gracefully.
I'd say if you're not looking to spare expenses get a good LGA 2011 (4930K, or other some such CPU) processor and board. They'll cost you more as it's an expensive platform, but would undoubtedly handle your cards better. The 4770K I'm sure would do fine as well, but it's tough to say. The LGA 1150 / Z87 chipset combination would be cheaper, and it would pack just as powerful of a punch.