10,000s of users

I’m about to setup a WP site where
a) User creation and capabilities are effectively managed elsewhere
b) I have an initial load of 35,000 users, and can expect 100s of users to be added/deleted in bulk every few weeks. And the odd single updates on an adhoc basis.

Does anyone have any experience with this level of users? Will WP just handle it, happily? Or are there any known pitfalls for me to look out for?