The experimental intensity stuff is interesting!
For my R9 290, I have used intensity 20, which gives stable 898kh/s average. On intensity 21 I get slightly over 900kh/s, but much more rejects. I think this is because the hashing function takes double time with +1 intensity, right? So when block changes it is more likely that the GPU is still hashing the old block.
290 has 2560 shaders, so equivalent value for intensity 20 should be 409.6.. I tried 410, and it gives exactly the same hashrate, as expected.
But if I lower xIntensity to 400, I get 901kh/s and less rejects than with I20! I guess there is similar "sweet spot" finding necessary now with all my other gpu's as well..
400 seems to be the magic value, any lower or higher will lower the hashrate.
Edit: bah, also 380 gives 900kh/s+, but 390 is slower..
This is going to take the whole day trying to find optimum..