A couple of years after Campy Ergo came out, I was in a club with a guy who rode a 531 Colnago with Super Record and (pre-indexing) downtube friction shifters. At the gathering before the start of one ride, I happened to be behind him and noticed his rear cluster looked awfully 'busy' so I counted. Ten cogs. So I (naively) asked him how he managed to run 10 speeds with shifters from the 6-speed era. And he answered, "Friction shifters don't know how many gears is back there."
I've lost touch with him but I'd wager that if he could find a (vintage) mid-length S-R rear derailleur, today he'd be running a 12-sp cluster on the same bike.
6x2 is enough for me.
I still have a colnago, a pinarello and a few others.
My favorite was a pogiagli, but like the dog I hit it was bent in half