Just realised that for at least the last 3 weeks my i7 4790K has been running at 4.6GHz, with the modified (2x bracket+2x through board removed, bracket askew) Coolermaster Eclipse running silent, and even at full sustained load running at only 1900RPM (which is just above its manual silent setting of 1800RPM).   Not bad considering the cooler only cost me $25, was first sold back in 2006 and is being used with cheap 6.8mK/W thermal compound.

Might bump it up to 4.7GHz, since 4.8GHz @ 1.35V is pushing its limits of stability.