My guess is an i7-3770K, unless a set of 20thread server processors have found a new home

It will be interesting to see if there is much performance (per GHz) gain this time for crunching. Some reviewers have IB as bringing only ~10% more performance than present 32nm models. While the CPU draws less Watts I think there may not be as much of a performance per Watt kick as some think. The motherboard and other components probably wont offer any significant efficiencies, especially high end boards competing against each other for top performance. So a mid to high end IB system is likely to only gain ~20% in power efficiency, and that's without a discrete GPU. While there is some minor discrete GPU increase in performance it's certainly not worth upgrading from SB, well, unless you have 3 or 4 high end PCIE3 GPU's to support.

Interestingly IB is supposed to support OpenCL on its integrated GPU! Prior to IB Intel only supported OpenCL on it's CPU. I think it's unlikely that the Intel HD Graphics 4000 will perform well relative to AMD's APU's and we will have to wait and see if it works here (or if it's even worth using). My guess is that when IB arrives Boinc will not recognise it as an OpenCL device, so the first up-takers will have to wait for an Alpha client to test.