Ok, one burning question, re rear derailers: "Within a given brand/style of rear derailer, all 'speed numbers' are generally interchangeable. This applies to all indexable models, basically everything manufactured since the around 1990." -- So what *is* an indexable rear derailer? It seems to me that if a rear derailer is able to shift through all the gears using a friction shifter, it should also be able to do so with an index shifter.... The barrel adjuster on newer rear derailers I'm sure helps make it much more reasonable to keep things in adjustment, but other than that, is there really a difference?

Thanks again, Sheldon. You & your website continue to be invaluable cycling resources.