Does anyone have any recommendations for ways of testing the performance of a game (in this case using XNA) on different machine specs? (cpu,memory,graphics card) . My development machine is reasonably high spec and I'm concerned that it's hiding various problems that would become more apparent on other machines (I have some evidence this is happening with a tester but we're trying to figure out roughly where the problem lies). I know that the ideal solution would just be to have a range of different machines at different specs, but as this is just a friend and I working on stuff for fun thats a bit over the top. Is it possible to setup vm's with limited resources to test this, or does anyone have a recommendation?
Not really true - lots of stuff in bullet is non virtual on purpose for performance reasons, I've found it's definitely much easier just to add stuff in directly and a lot of people seem to have custom bullet builds.
Microsoft do seem to be trying to kill it off, they've recently split the creators section of their site into phone/indie games sections and in the process broken nearly every single google link to the data there. The general impression is that they're just trying to make it fade away without making any real announcments on it. All their current efforst seem to be on Windows Phone and Tablet work, and while XNA is valid on the phone for now I really get the impression they'll start pushing more forcibly to c++.
Having saiid all that XNA is still a pretty good framework and the with some of the replacements mentioned below you'll be able to get a lot of stuff done with it very easily.