Prime95 for Mac Timer Issue
 

Not sure if this is just a timer issue or it's actually taking longer, need to verify, but once Prime95 on Mac loses focus for an extended period of time, iteration times increase by a substantial amount. I leave it running during work and check in every once in awhile, for the numbers I'm working on it's ~12-13 seconds per update (when it has focus). However, if the program doesn't have focus for awhile, it starts saying ~22-23 seconds per update. As soon as the program regains focus it starts once again saying 12-13 seconds per update. I think it's just the timer value being used is unreliable, I don't think it's actually losing processor time.

This is Mavericks saving power by down-clocking the CPU when the foreground tasks aren't using the processor. I found an OS call to disable this feature. There will be a new preference item in 28.5 build 2 (not out yet).

In the meantime, make prime95 the foreground task whenever you leave your computer.