I've been tasked with expanding the list Windows platforms that our software is "officially qualified" to run on. Currently, it's 32-bit XP, and 32/64-bit Windows 7. I have to add to the mix, Server 2003, Server 2008, and Vista, in all available 32- and 64-bit flavours, with a mix of different editions (professional, enterprise, ultimate, etc) and service packs.

That adds a significant amount of testing that we have to do (5 release branches * 2 architectures * 25 operating system flavours * 1.5 hour and growing test suite) in a 6-8 hour overnight window of time. If I get my math right, that means worst case we have to have ~62 VMs simultaneously running our test suite, which, naturally, is bandwidth and IO intensive. Obviously, any way we can cut this down would be a great boon.

The most obvious is to skip all the different editions. Can anyone say with certainty if different Windows editions behave identically? For example, if I test on 32-bit Windows 7 Professional (which would be the lowest supported edition), do I really need to test on 32-bit Windows 7 Ultimate? Most of the differences between editions appear to be things like networking services, and bundled applications, which wouldn't affect our product, but are there kernel/dll differences between editions, as well?