While I understand why you are concerned, you have to understand that if Intel wants to hit a certain TDP, they have 2 options on a given node. They can either reduce the core count, or reduce the clock speed of said cores (assuming we keep cache sizes/iGPU shader counts etc consistent I am referring just to the CPU side)..Since we all want an Octacore in non Xeon trim, then Intel has to keep the clockspeed down to hit a certain TDP..
Now we all know even the worst silicon has headroom over the "stock" clocks, it just depends on how much voltage you are willing to run through it. Intel reserves clock speed so that they can offer some "value" in the form a refresh (see the 2600K to 2700K, 4770K to 4790K etc)..
Lastly, since they are K SKUs, it is quite easy to go into the BIOS and adjust 1 setting to increase the clockspeed via the multiplier, even if you want to keep the stock Vcore..You will most likely be able to squeeze out at least a few hundred Mhz more unless these chips are complete dogs..
I was 99% certain I was going to move to X99 and get the 8 core flagship part (never owned an "EE" part and while I don't want to drop 1K that is the only way to play these days) when they were announced, the closer we get to launch the more I am worried. If the 8 core parts do come in @ 3Ghz stock, and we assume the best parts are able to reach a 50% OC (which is a lot), then we are looking at ~4.5Ghz for the platinum center wafer cut chips..
While I have the cooling to take said CPU to that level, finding one is going to be the challenge..And then I have to look at losing 200~300Mhz of single thread performance (vs my sig rig) since the IPC jump of Haswell isn't much over Ivy..I think the 8 core parts are going to reintroduce the old "batch hunting" we used to do when trying to source the best OC'ing parts, since we know the 8 core SKUs are being harvested from 12 core dies that don't make the cut..
A 12-core chip that has been harvested into an 8-core chip may clock just fine. The reason why the cores were disabled may just be due to a defect in the cache, one of the largest areas of the die and the most likely where a defect will occur. Even if a core is defective and is deactivated as a result, it may not be indicative of an inability of the other functional cores to overclock well and may actually overclock well (it may have been a high clocking die, except for a defective core or two). It's really tough to say for sure, though, as the reasons why a core is disabled are very numerous and more than one may apply to a given die.