Personally, I had my
[email protected] on air. It was a Noctua NH-D15. You should be able to get to 3.9 on half decent air cooler? Hell, I could even run 3.8 on auto volts, and that was fine!
Other thing to do, if you have G.Skill B-Dies, you really want to get 3200 C14, for me that was the sweet spot...