So, you had 1050 real users taking an exam at the same time? The definition Performance_FAQ#How_do_you_define_.22concurrent_users.22.3F is a bit different, still very interesting. Did you monitor the stress on the system, CPU load, memory usage, etc. during the exam?
So many VMs sound complicated. Do you have a schematic diagram of the setup? Is it related to the Server_cluster as documented.