11.81V is excellent during load. What are your 5.0V and 3.3V rails under load? Did you remember to plug in the 4-pin (or 8-pin) CPU power connector(s). These are near the top-center of the motherboard and augment the CPU power draw from the 24-pin motherboard power connector. Does your system crash to a blue screen or shut down completely?

I got this from the EVGA forum: ATX standards specify that power supplies have a +/- 5% maximum variance tolerance on each rail. For each rail, the voltages should be in between:

5 VDC
+4.75 V to +5.25 V

−5 VDC
–4.50 V to –5.50 V

+12 VDC
+11.40 V to +12.60 V

−12 VDC
–10.8 V to –13.2 V

+3.3 VDC
+3.135 V to +3.465 V

+5 VSB
+4.75 V to +5.25 V

I believe if you have a Corsair Power Supply, the guaranteed tolerance is a function of the series (bronze, gold, platinum).