I5 2500k vs i7 2600k?

The main difference is HT or Hyperthreading, the OS will see eight cores instead of four.

of course you have the 2mb of level 3 cache.

I'm going to use the rig for gaming, since (afaik) games dont utillize the most out of 2+ cores there is little point in getting i7 2600k?

Yeah, if it's just going to be used for gaming now and in the future then a 2600K is pointless, the extra 2MB of level 3 cache that the 2600K has over the 2500K may help in a multi GPU setup but then again it might not.

Well... the i7-2600k is 100MHz faster at stock speed.  

Unless you are going to be using programs that can take advantage of HT, you are better off getting the i5-2500k.

100mhz does not a trouser tent make.  

Oh my this question again...  

Get the 2500K, take the money you saved from the 2600K and invest in the increase of your graphics card budget. Getting a better graphics card with the 2500K than the 2600K with a less-potent GPU will last you a LOT longer, and deliver a much more powerful gaming machine from the ground up.