Is the member module designed to have tens or hundreds of member groups?

I think you’d be fine on the front end, the number of necessary queries should be pretty much the same, but the back end (control panel) might present a bit of a problem, trying to manage such a large number of groups. There could well be performance or display issues there. Those should not affect your regular site users, though. That said, I’d simply give it a try on a local development setup and see how it goes.

Thanks for the reply,

The creating of the groups would mostly be automatic and duplicated from a ‘master’ group, where any future changes would just be a MySQL command

The idea of having the member group as the determining variable was for finer, more restricted control over what the user sees.

Revisiting this, I may be able to use custom fields for the control I’d like.