I7 3770k (though I've heard these can run really hot)
this rigs' main use will be for gaming. I want to overclock to around 4 - 4.5 ghz
Which would be best for gaming and overclocking?
Any of the above should be more than fine and there is not a huge difference between any of them in gaming, unless you want to game using the IGP (I wouldn't recommend that ) The i7-2700K and i7-3770K are very similar chips and perform nearly identically. The main difference between those two is that the 3770K costs a little less. The i5-3570K lacks HyperThreading, 2 MB of L3, and a hundred MHz, but you shouldn't notice them when gaming. Overclocking any of these will be fairly similar as far as speeds able to be reached. The Ivy Bridge 3770K and 3570Ks are built on a smaller 22 nm process as opposed to the 32 nm 2700K, but the Ivy Bridges get seriously smoking hot when you up the voltage much at all...so you end up with a low to mid-4 GHz overclock before things get out of hand either way. I'd go with the i5-3570K just because it's the least expensive option.
The big deal on 2700k or 3770k is hyper-threading. What that is useful for is video rendering... ie: converting video formats (not gaming). You could go a notch down to something like a 2550k or a 3570k.
If you are going to Overclock aggressively without water-cooling you will want a 2550k or a 2600k/2700k.