I recently bought a Powermac G4/553 DA model and it's really responsive with Classic. One of the last Classic-compatible models. But it feels really simple compared to any modern OS.
And something I've forgotten in 20 years since the last usage of Classic: There's no real multi-tasking. Uncompressing zip or sit packages basically blocks the whole OS until the work is done.
Oh and other things taken for granted nowadays I've forgotten: one can use _the same computer for other things when scanning photos_. Then even the fastest computer was blocked until the scanning was completed :D