Ran mine at 4.2 for the best part of a year with stock cooler, temps ok for normal use eg playing bf3, but anything like prime will push it beyond what I'd be happy with. worth mentioning I had a 12cm fan on the back, 2 14cm on the top, 2 9.2cm on the front, 1 14cm on the bottom + 12cm in the psu on the bottom 
