Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
You are right of course, the power output does indeed increase with revs, sometimes to 14v. The headlamp filament is a crude affair that glows white hot by the heat created by the current passing through it. The higher the voltage, the brighter the lamp. If the voltage gets too high the lamp will blow.
LED is deffinately the way to go.
In the UK your bikes are subject to periodic tests, I believe. Any risks there?