Also, poor performance of UUIDv4 primary keys is most related to how write heavy your table is in the first place, and in particular how insertion heavy it is.

Also, poor performance of UUIDv4 primary keys is most related to how write heavy your table is in the first place, and in particular how insertion heavy it is. In theory your users table shouldn't be very write-heavy, even if it may be insertion-heavy compared to other writes.