Thanks. 

I only started this research because I got a "Red light" on one of them and it was running at half-rate.  Its powered with 1500W of EVGA gold PSUs (twin 750)...  Was thinking it might be power related I cut it down to -2.  No red light.  Now set it at -1 and no red light after 8 hours.  I'll let them run for 24 and then decide what to do.

I may go back to 0 again.  The units are running at 33/85C on average so not too bad....