so what's the advantage of the i5-2500k over the i5-2500? some kinda turbo boost?
The 2500K is unlocked so you CAN clock it, the 2500 cannot be clocked. There's no point getting a 67 board with a 2500 for just that reason.
If you never have any intention or desire to OC, you can save some bucks with a 2500 and a 61 series board. If you want to OC (and the performance gains are nothing to sniff at) you have a slightly pricier option, but once you OC it, you void your warranty. I believe you also void the warranty on most motherboards as well.
So it's really just a matter of what your objectives are, that's all.