Although we have only briefly tested the effects of shader clock overclocking, I think that it is quite clear that increasing the shader clock speed really has a limited impact on performance. This is a shame, though with word of the ability to asynchronously overclock the shader clock sure to spread, I thought you may be interested to see the effects regardless of how insignificant their impact may have been. When it comes to overclocking the best gains can still be seen by increasing the core clock and then the memory. For those that want to make every last frame count shader overclocking is just another way of getting a tiny bit more at no cost.
Check it out at Legion Hardware.