I have been using BB .4 and is had been very good to me. I first ran p3's 1ghz processor and then switched to chevy's 1ghz. I did not notice any difference between the 2 kernels.
Only complaint is the battery life on .4. I had amazing battery life on the last BB 2.1 rom but this one has been running through the battery much quicker. Same apps and same widgets. I use profiles in setcpu as well.
I love the rom. I do wish playing .wav files in froyo was resolved though...