I do ride 40x14.

I don't really know anymore what speed I maintain since I took off the computer. I do know it's about 75 gear inches and works out about the same as 42x15 on a road bike, perfect for cruising. fast. i.e, steady 20+mph on long flat stretches.

I changed out my commuter to 40x16 recently -- and that slows things down a lot but slower feels safer, especially in midtown. thanks for asking.

ps... pedaling super-high cadence also seems to let drivers know you're moving fast, working to go with the flow of traffic. It has to be the most obvious visual cue: you're not in the same kind of vehicle they are because you're pedaling like a madman. But what's this got to do with lights? Uh... getting things back on topic - I just put some 3M safety-of-life-at-sea (solas) tape on one of my crankarms for enhanced visibility. The cool thing about this stuff is that it even comes in black, and can be used to finish handlebar wrap in place of regular tape.