Upgrade to Haswell or Ivy-Brigde?

So I want to upgrade my computer. I currently have an LGA775 socket, running a dual core pentium E6500 cpu, and I was wondering if I should upgrade to Haswell or Ivy-Brigde. I do plan on overclocking, and the main use of the cpu would probably be gaming. Probably the range of $400 would be the sweet-spot for me.

Having said that, which one should I purchase?

If you want satisfactory overclocking results, go Ivy. It appears Haswell is fine for anything up to 4.3, approximately.

Apparently Haswell and Ivy Bridge have similair performance when it comes to gaming. Productivity wise, Haswell smokes Ivy Bridge. Plus, Haswell runs extremely toasty.

So, if you were going to mainly game on this system, I would go with an Ivy Bridge processor. i5 3570k or i7 3770k...

So since I want to overclock, the best choice would be Ivy-Brigde because of the temperatures Haswell has, right?

Yeah, Haswell is ok for mild overclocking. Though, you could get lucky in the "silicon lottery" and maybe push 4.5-4.6. 

If you want to view the platform as a whole, Haswell does have the better motherboards. However, that shouldn't matter in your interests. Then again, if you installed a custom water cooling loop, Haswell could make for an attractive upgrade.

Keep an eye out on the Ivy Bridge chips dropping in price.  The only reason I can see going with IB is for the last-gen lower price.