In a real environment, the 500VMs wouldn't be identical. The customers would use them differently and would tax them in different ways. Is it possible for you to copy real, in-use, VM from customers' backups? Have you deployed Win2008 core in VM used by your customers?
Correct, they would not all be identical in the real word, but that's OK for what we're trying to prove. We have ways to vary the latency in their response to our WMI and MS-MAN queries, so we can vary our own load if when needed. We've already established that WMI doesn't handle latency very well and is a chatty bastard. We're implementing functionality to solve that by using WS-MAN as an alternative if customers want to use it.
We rarely have the option from customers for them to give us a working copy of their system. Many are banks and financial institutions that won't even let us webex or remote desktop to their systems (with very good reason). Even in times when we visit on-site, we can't take cellphones or electronics into their buildings.
No, we've not deployed a Win 2008 Core VM used by our customers. We're mainly trying to answer if our own software can handle the mass number of discoveries of these systems and extrapolate some numbers. This tests assumes they're all identical and can respond adequately and similarly. A customer's system would respond in different amounts of time as you've suggested, but that's not what we are testing for right now. If we can't handle the discovery in a system that does respond consistently, then we're not ready to handle the discovery in a system that varies its responses.