extreme is just fine champ. wont hurt a thing. i have the same board, have had it on extreme for since out of the box (6 months now). no problems thus far.
I did 5ghz runs, and had to go up to 1.5v. But there's single run voltages, where doing that for 2 minutes won't do any harm...
Then there's keeping it at that 24/7, which certainly will do harm.
I personally wouldn't push more than what you have.
My chip for example, will do 4.5ghz at 1.205v. Yet needs 1.3v(ish) for 4.6ghz...
That's similar in most cases with Ivybridge, and it really isn't worth the increase in temperatures, and potential degradation to the chip for a meer 100mhz...
