In situations where dual CPUs can be fully utilized you should be favoring reliability more than with a 6700k. Leaving compatible processors locked, using EEC ram, and similar reduce the chances of something going wrong with the system. Anyone who has the workload for two processors needs the reliability not present when OCing.
This is to say nothing of the power necessary to OC two processors on the same board, as well as the heat on the VRMs.
The reality is no enthusiast would ever need two 6700ks (or similar), and those who have the workload for that many threads want something more stable.
The middle ground (I think you are looking for) is the Skylake-E platform on X99. High thread count, unlocked, and not server grade.