Recently news has been coming out that the Ivy bridge is actually worse at overclocking compared to Sandy Bridge processors, due to the extremely high temperatures at even relatively low voltages. Given that the underlying architecture is the same, you would expect the two processors to perform about on par clock for clock. Wouldn't this suggest that unlocked CPUs like the 2500k will actually have a better peak performance when overclocked, compared to the Ivy Bridge chips?
I would just take a wait and see approach. The tests that have been done so far were most likely only on engineering samples and not indicative of what the final product on release will be. Once we see a full sample size of chips out in the wild from retail, we'll know more. My hunch is that there won't be much, if any improvement though, but I'll just wait and pass judgement when its warranted.