So the answer is either i7-4790K for it's low memory access latency and high clock speeds or the i7-5775C for it's eDRAM? (paired with the lowest latency ddr3, probably g.skill from my experience?)
With stock numbers, I'm pretty sure the i7-4790K would win out over the i7-5775C; in particular, the 4790K has double the memory bandwidth, and officially supports faster memory, in addition to faster single-core speeds.
The serious question that would probably require actual testing would be the i7-4790K (still leading the pack in single-core stock performance in various tests) versus the newer i7-6700K (slightly slower clock, but newer with more memory bandwidth and official support for slightly faster memory). I would hazard a guess that the i7-6700K in a properly built system (taking advantage of memory speeds, DMI3, etc.) would pull ahead of the older 4790K for DF, but wouldn't bet much money on it. On the other hand, it's a newer chipset with some other advantages, and it's unlikely to be *much* slower for DF, so even the "worst case scenario" is pretty good.
If you're into serious overclocking (especially beyond what you can get on ordinary air alone), that's a specialist topic I'm less qualified to comment on. In scientific computing, which some days has a fair amount of similarities to DF in that it can be single-core limited and very heavy on the memory access, we need the workstations or cluster components to run rock-stolid for weeks if not months at a time, and can't afford to hand-pick chips or risk burning them out prematurely. Overclocking beyond the built-in turbo features is rare and limited.