Originally Posted by
WheelsNT
On the derailer choice, most shimano derailers (with a few specific exceptions) have the same geometry, so you don't have to look for a "7-speed" derailer.
I should hope I wouldn't have to be looking for a "7-speed", since we have 8 on the cassette! From what I can tell, the actuation ratio (cable pull:lateral movement) is what matters, and, as you say, is constant. Derailleurs marketed as '9-speed' seem to have larger capacities, due to the likelihood of having a wide gear range being higher with 9 sprockets, but, I'm sure it's not a hard and fast rule. We'll probably be getting the 43T tourney.