Originally Posted by
ThermionicScott
Long cage derailleurs came a long way between the 70's and 90's. My circa-1990 Deore LX shifted quickly and flawlessly despite having a long cage. I would rather have as much capacity as I could possibly need, than to get clever with a short-cage derailleur and hope I don't absent-mindedly destroy it while out on the road.
Yeah, I won't ride a bike with any potential of incompatible combinations of chainring and cog, especially with downtube friction shifters.
For example, I'm still getting used to the Huret Jubilee drivetrain on my Motobecane, and I've definitely accidentally shifted into big/big even when trying to make a conscious effort not to. It would be such a shame to let an accidental overshift or simple absentmindedness cause a major mechanical issue.