I'm interested in this thread because I have different set of issues - many with the Brompton older SRAM hub which provides 6 closer gears, and the newer BWR hub which has wider jumps, say the newer hub is slower. Mechanical efficiency seems near identical. That is counter to the single-speed is faster argument as on the BWR you're stuck in a particular gear for longer so less changing, more fighting through to hold a cadence, etc. Hence BWR should be about the same speed. That is, unless, the rider is taking opportunity of the wider gears to go slower up hills.