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
I'm actually finding with the 8-11 kernel that memory speed can be dropped down very low and still maintain optimal performance. I've got a total of 5 58X0 cards running, and they're all perfectly content to max out the MH/s at 150MHz memory speed.
So while I've found that phatk 2.2 can do about 1-1.5% higher than 8-11 at the same core speed, phatk likes a memory speed up around 430MHz for optimal performance. So with that memory speed drop, I'm seeing about 2-3C lower core temps on my cards...or about 20MHz higher core speeds for the same temps, which more than makes up for the performance gap.