1600x is there a temperature offset? Also what are the recommended voltage on OC?

People say there is a 20C offset. Though mine idles around 35C i can only assume either the software subtracts the offset automatically or the offset never existed or was removed with the latest drivers? Just wondering if i could get some direct facts about it so i know whats what. Also I'm running my 1600x at 4Ghz 1.35v stable, is there a recommended voltage to run 4.1 or 4.2Ghz? Thanks