Hey KMS,
You should chekout the SRND for CCM4 http://www.cisco.com/application/pdf/en/us/guest/netsol/ns268/c649/ccmigration_09186a008022147a.pdf
There is a section in there entitled 'Cisco CallManager Platform Capacity Planning' (Page 186).
Basically is says that if your server meets the requirements then you shouldn't need to verify it... The server that you are using is classed as a High-Performance server and allows a maximum of 7,500 users per server.
I think that you should be fine, however the TAC have access to the 'Cisco CallManager Capacity Tool' which should give you the exact answers you want, so I would confirm it with them.
One issue that is worth considering is; what happens if all users are logging in (or out) around the same time, say 8:30am or 5.30pm...
A typical login to Extension Mobility makes two HTTP requests: one to query the initial login state of the device, and another to log in the user on a device. Similarly, a typical logout also results in two HTTP requests.
Hope this helps...