They're exactly the same, it's just that the K version has an unlocked clock multiplier for easy overclocking. A stock i7-3770 is perfectly capable of running games at any settings as long as it's paired with a good graphics card, so if you're not into overclocking, get the non K version.

+1 for RyunV. Either the k or the non k is a great high end processor. If you have no interest in overclocking, get the non k version.

But whatever graphics card you get will dictate how good of gaming performance you get. Nowadays the graphics card is much more important than the CPU.

The K means it has an unlocked multiplier, so you can overclock it easier. If you aren't overclocking, there's pretty much no difference.