I've been running the 57/63's for a year now and I love them. I'm sure the 56/64's also work well, but I've never felt like my sled was over-geared with the 57/63's. There's only about a 3% difference in ratio between the two, so I'll bet any difference in performance is minimal.
Rode with the new gears today. Much improved. Don't notice much difference in top speed but now need to get a few hundred more RPM. Went from 7450 down to about 7250. Still much better bottom end. Not KK snap but it's getting closer. Don't think even going 54/66 would be too low. Stock is way too high. Maybe some secondary changes might be next.....
Thanks Catsled for all your input.
No gears yet, I don't think I can ride today the misses is making me spend some time with her, isn't sleeping in the same bed enough ???? I will call you later.