Joined: Jan 2010
Posts: 9,835
Likes: 1,816
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
I've used SIS 6-speed derailers with 8s cassettes, no problem and the indexing was identical as with an 8-speed derailer.
With 11 speed, Shimano changed to a longer cable movement, but I have yet to see published what the actuation ratio is, and whether it might be a good substitute for an earlier Campag rear derailer from the 8-9-speed era. The very small cable movements of increased number of cogs caused the traditional SIS actuation ratio to max out with 10-speed systems, so for 11-speed Shimano increased the cable travel to restore derailer movement accuracy.
I would like to at least get my hands on one of these Ultegr 11s derailers, to test it out with older Campagnolo Ergo shifters. They're about $100, but there is a swap-meet coming up...