I have an update on this. I requested a trial license from support to double the number of users on our license - this was issued with an expiry date, and allows me to track peak usage.
Using the trace logging that @Bart_Elia explained above, I have been able to demonstrate that the system is consuming 175% of our usual license count. Again, this is only after upgrading from 10.1.600 to 10.2.300.