Yeah I found 9/20 laggy as hell. 9/6 seems much snappier. I still can't tell what the main differences are (other than some subtle differences like icons)
I did notice the keyboard is different though..I couldn't access XT9 mode on the 9/20 for some reason and it was using a newer keyboard, like the one on the Touch Diamond 2 (I think...).
Anyway happy with 9/6 so far..snappier, I can use XT9, and I can actually dial out. Can't wait for the next release that hopefully fixes the bugs in 9/20.