We prefer overclocking from the motherboard firmware, though. Using simple multiplier and voltage adjustments, we achieved a Prime95-stable 4 GHz clock rate at 1.425V using Asus' Crosshair V Hero (that was with load-line calibration set to Auto). The highest temperature we saw was 82°C during our stress test.
Of course, if you're using a cooling solution less capable than our Corsair H100i v2 at its maximum fan/pump settings, overheating could become a problem. AMD predicts that most customers should see somewhere between 3.9 and 4.1 GHz across all cores, and suggests you stick with a 1.35V ceiling if you want your chip to last. Although core voltages in excess of 1.45V are considered sustainable, they'll have a more pronounced effect on longevity.