[citation][nom]dragonsqrrl[/nom]While further integration of components that once occupied the motherboard, such as VRMs, and finer control over clock domains is sure to benefit the lower end of the TDP spectrum, the effects of these enhancements on desktop parts seems far less advantageous. It even seems to have a negative impact on overclocking potential.[/citation]
While extra integrated stuff with the associated TDP certainly does not help with overclocking, you also need to keep in mind that other architectural changes such as the more complex branch prediction, more complex cache, wider paths between caches, deeper out-of-order buffer, extra issue ports, etc. all also add complexity that will slow down critical paths and cause lower maximum achievable clocks.
Nothing is free. Haswell's slightly higher IPC comes at the expense of complexity and that extra complexity cuts into timing margins which translates into lower overclocks since there is no die shrink to hide the increased complexity hit.