Isn't it Brian May (of Queen) who used an old sixpence as a plectrum?

When I was playing in a soul band, I used a very heavy Stubby "2" pick on my Tele. It gave a great sound and had had plenty of power. Stubby "3" picks are even heavier - and probably wouldn't be far off a small coin in thickness.

But I would question the sound - and the extra probability of strings breaking - of metal hitting metal...