To add another anecdotal data point (keep in mind the saying "anecdotes are not data"), I used a Watson and both plastic and metal cartridges all through high school without getting any scratches over several hundred feet.

I wasn't a super clean freak back then but did always blow out the cartridges and ruffled up the light traps before loading. I also never tried to overload, it just seems to be asking for trouble to force feed film into a tight package and not expect binding and extra pressure to take its toll.

And so in summary: I blew out before setting up the load and I never forced or spooled more film than was designed to fit in the dubious pursuit of "just that one more frame, c'mon!" Seriously, carry one extra roll and that makes up for up to eight cartridges crammed with more frames and the additional stresses that may or may not cause problems.