Basic drivetrain queries for the roadies...

For audaxy riding, I agree with all the compact advocates. I'd also say Dammit's claim of spinning out a 50x11 downhill 'early' is very subjective. That's basically a 120" gear. Spinning out in my mind means around the 180rpm mark (I can go faster, but it's a bit nervy) which is 64mph. Even 140rpm is 50mph.

Yup, subjective it is. This was going down Ditchling beacon at an indicated 57 mph, and I cannot spin for toffee. Please see stupid gear on commuting fixed for proof.