Originally Posted by HeadlessKnight
In games that scale well with HT such as Crysis 3/BF4 the i5 2500K @ 5GHz will match your i7 2600 @ 3.9GHz, if you managed to get the 2500K to 4.5 it will still be slower in those examples than the i7 at 3.9, but 5GHz is a pretty high oc and most 2500K won't make it this far with 24/7 settings. In games that do not scale well with HT or at all (which is the majority of game and apps btw) the i5 2500K even at 4.5 it will wreck the 2600 at 3.9. So there is a tradeoff based on the apps you use. you will most likely benefit from the high clocks in heavily CPU bound games and emulators such as PCSX2.
Well, how much retaliative performance gain can you really see? Going from 3.9 to 4.5 (a fair OC) is only about 15% increase in clock speed. I personally would just keep the 2600 because of hyper threading. If trends keep following the path the industry is heading, more cores WILL be better. Especially with all this DX12 stuff.
It just depends if 120$ is worth it to the OP. If it's strictly gaming, then yes, the i5 would be better for sure. Especially with the majority of games released as of today.