Power comparisons

I read that Sir C.Hoy puts out 2,300 to 2,500 watts during his 200 metre sprints and I recall some of the TdeF riders averaging over 450 watts for long stages.

There are various ways of measurement - at the pedal, at the crank, at the rear hub and on a turbo trainer - but what's the baseline measurement to do reasonable comparisons between riders?

Presumably there different tests and figures for endurance riders and sprinters, so you couldn't compare Sir Chris with Bradley Wiggins CBE. Does anyone know what they are and how we, mere mortals, compare? Nerd