Originally Posted by
PlatyPius
I've never measured. I just remember the propaganda from Shimano in the 90s that said that "everything is narrower" and that you "must" upgrade everything. It wouldn't surprise me if there's no difference at all.
I am kind of surprised that you don't know this, given your experience, but most of Shimano's 'compatibility rules' are complete BS (bike silliness).
You don't need to match number of speeds of chain with derailleur any more than you need to lather rinse
and repeat to make shampoo work.