Depends on what you want to spend in reality. Past an I5 (which can be overclocked like a beast) the price to performance ratio is pretty bleak. Yes an I7 is 10~15% faster and does have some performance benefits, but is it worth the approx 33% price increase, not to mention the 3930K price is even more. I can see you wanting to buy the best processor to stay ahead of the curve, that would be the I5 right now.
HOWEVER! The big thing here is 1 CPU (3770K) is LGA 1155 and the other (3930K) is LGA2011. LGA2011 is the ultra high end performance system systems and have the benefit of 8 RAM slots, 2-3 full 16x PCI xpress slots and cost more. People who I have built these systems for are creating multiple virtual enterprise systems, SharePoint Server farms, things of that nature. These are business professionals willing to build a 2.5K system (at cost).
I agree with the previous posters, get an I5 (or I7-3770K) with an LGA1155 motherboard. Save your money for a better GPU and SSD. Those will give you way better bang for your buck. Also, pick up a NVidea if you are doing rendering and use that CUDA core.