For our manual overclocking tests, we used AMD's driver tuning tools. Our best results are as below.
Interestingly, AMD has capped both the GPU and memory frequency sliders, to 2975MHz and 2400MHz respectively. I was able to put both sliders at their maximum values without instability.
That saw average clock speed increase to 2957MHz.
Performance didn't really increase by much at all as a result of this overclock, with the one exception being in Hitman 3.
Power draw did bump up by around 14 Watts or so, however.