My 990 UD5 is a brutish board ( rev 5 I believe) hardware wise but has a pretty awful bios. Gigabytes software OC utility is about the worst I've seen.
Be sure to be running the latest bios as it will give the best Vishera support.
Board shouldn't hold the chip below 4.7 ghz , cooling , power or settings will.
I made the 24/7 5 ghz club with mine pushing a FX 9370 @ 1.6 volts.