Testing older AMD drivers, by putting the AMD OpenCL (amd_opencl*.dll and amdocl*.dll )files in the same folder as the miner:

13.4 - Gives out of memory errors (GPU memory allocation failed)
13.9 - Similar performance as 13.12
13.12 - Baseline
14.4 - A lot slower, about 25% and gives error codes at startup
14.6 beta - A lot slower, about 25% and complains about "bad performance mode" at startup