Chiming in-
I don't have any idea of all the compatibilities, but-
I know the new RM-30 for example, will NOT fit an M-570. (or old EXAGE hubs)
I tried to put the 7 speed body onto an RM-30 hub to make an extra strong rear wheel. (along with an OC rim)
I was going to use 8 of 9 on 7 for my grocery getter.

Just use the 9 speed hub and add the 4.5mm spacer.
Many NEW 7 speed are doing exactly this. (maybe all?)

http://www.amazon.com/Wheels-Manufac.../dp/B001CJVLWO

You DON'T get a bag of 5! Best to check with your local LBS. They "should" have them. Mine seldom does though.