Speed? Did this one already , look it up.

Florian Schlumpf's High Speed Drive gearbox crank has an overdrive gear in it, so the chainring turns 2.5X for every rotation of the pedals (Small gear acts huuge)

But remember, on Earth, you have an atmosphere , and air resistance goes up by a factor of 4 X as you double the speed ..

Yes Bike Friday hyper fold Tikit is the bike that folds the fastest,, once you get the knack, it's just a few seconds and gravity does most of the work.