I made an interesting discovery during my own tests with the new kernel version. I had to up the memory clock of my 5870 from 200 to 350 MHz in order to achieve the highest hashing values. Another thing to mention is, that I drive a Phenom II X6 1090T with only 800 MHz for every core, due to power saving, while mining. If I let the CPU use full speed, MHash/s goes even higher, let's say 3-4 MH/s.
Conclusion: Perhaps you guys should try to raise your mem speeds + experiment with CPU clocks, too. I know it has to be a good balance, so that higher MH/s values are not eaten by higher energy costs.
Dia
My card RAM is already at 360 MHz and I've tested but I can't find a better frequency for the RAM at my core speeds if I'm only interested in MH/s.
As for CPU usage I've not touched my CPU settings at all and the miners only use about 0.4% each. I even removed the fan from the CPU and placed it to cool the back of my hot card (the heatsink on the CPU is not even warm). I'm assuming significant CPU loads is a Windows thing.
What interests me is how SDK 2.1 seems to be better at higher clock speeds whereas SDK 2.4 with your kernel is better at moderate speeds (940 MHz or below). I admit I have little data on this but if anyone else gets the same results it would be interesting to know why.