Okay I was searching for some additional stats for poclbm. What I found was the following:
I'm quoting here:
Using phoenix you find both kernels in the kernels folder (I know, kind of obvious, isn't it?! ). This modification works for both kernels but only if you're using BFI_INT.
You can go to phatk's kernel.cl file (don't worry, it just sits there in the open, no need to recompile anything), find this line
#define Ma(x, y, z) amd_bytealign((y), (x | z), (z & x))
and change it to this line
#define Ma(x, y, z) amd_bytealign( (z^x), (y), (x) )
Once you've done it, restart the miner.
My results: Cayman cores gain ~14MHash consistently. 5xxx cores should gain even more.