Any question answered...

Overtighten the clamp, bang goes the frame however.

My roadbike takes a band on, I would prefer braze.

On that note (sort of), if I got cranks that could take both a normal (53/39) pair of rings, and a compact (50/34) would I need to move the front mech up/down when changing, or would that be ok left where it is?

Uh, yup..... if you like crisp, reliable shifting, you need to maintain the gap between big ring and outer cage between 1-4mm (depending on religious persuasion, and hemisphere).