On top of booting faster via CP/Extension caching, I wonder if
Startup Doubler also improves responsiveness, if at all.
Edit: Another thing to wonder is what is the "minimal" OS 9 installation we can have (in terms of CPs and Extensions) while still able to do most things comfortably. Or, in other words, "optimal" installs. For me, GPU drivers, Ethernet, USB Overdrive, FinderPop and Default Folder should more or less cover most of my needs... Too bad StuffIt also seems to require an extension (StuffIt Engine), since programs like MacZip still do a great job without any of that.
Makes me want to have multiple System folders. I.e.: "Fast", "Balanced", "Full".