I've not overclocked mine. I don't see any point really.
I did run a load of benchmarks on it and at first felt a little disappointed. Then I ran the same ones on my 670 SLI and realised just how much higher they were on the 7990.
I played BF4 for two hours last night and saw 70c/58c on the GPU cores. Awesome sauce.
The constant search for extra free performance?! It's an addiction, as is benchmarking!