You got real lucky, most 6300 i see around here don't pass 4.4ghz/4.5ghz
hell just for comparison, i got a 4300, 6300 and this 8370 (bought a 8320, they sent a 8370 not complaining) on Amazon, the 4300 does 4.9ghz 1.381v/5ghz 1.44v, the 6300 does 4.4ghz 1.42v (gave it to my father in Portugal, temps there are a problem for OC so 4.4ghz is not a bad 24/7) and the 8370 does 4.7ghz 1.428v (couldn't test them any higher because i only had a NH-D15 at the time).
You just need water even just a CLC will get it done, Oh you knew getting back into Air your going to be realistically stuck at like 4.7-4.9ghz with the D14, I don't see how the D15 is an improvement about the same thing Probably stick some meaner fans on it etc, but everyone needs a good air cooler you know.
I wouldn't touch one without living in a reeeeeeeeeeeeeeeeeeeeeally cold place like Canada or Iceland for example...