The unlocked processors that the GA-Z68XP-D3 supports:
The Core i5-2500K is cheaper by about $95 because it doesn't support Intel Hyper-Threading Technology. If you're on a budget this is the one to choose unless you really need the eight thread processing of the Core i7-2600K.
Ahhh sorry, that's what I get for trying to go from memory after looking at confusing motherboard serial numbers for a couple of hours
Yes the unlocked processor at the top of the i5 range was the one I ment, so that would be i5-2500k.
If you're going to be using the stock heatsink & fan that Intel provides with the processor, just make sure that your processor's temperature doesn't exceed 75°C when overclocked. Back off on the overclocking if it does get too high.