Cheap TIM held Ivy back, and IIRC its pretty much been confirmed that Intel is going back to solder. And with the extra time of 22nm under their belt plus other overclocking friendly features being added in to the new architecture, I'd almost be willing to bet 5GHz will finally be a new norm for the enthusiast willing to spend ~$100 on cooling
However I'd bet against IPC improvement being that high, it'd wager it will be closer to 10% at best
It isn't the quality of the TIM that holds IB back; rather, it is a matter of how thick the TIM layer itself is.
Also, unless Intel has internally changed their decision on the matter, last time an Intel individual talked with me about the topic the plan of record was to package Haswell the same way as they package IB (no solder for desktop socketed cpus).