Wow your build is almost identical to mine except you have a different Mobo. I've got my 4670k up to 4.4Ghz without any problems. 4.2Ghz at 1.1V was stable, and 4.4Ghz at 1.15V was stable as well. Every CPU varies though, so you'd have to play around with it a bit. At 4.4Ghz I hit 75 degrees C at the most during intense stress testing.