Replying to: Adrian Roselli
Did you play around with IE conditional comments to load your IE7/8-only CSS? Other browsers ignore them, so no additional requests, and IE7/8 will ignore media queries, sparing them the request(s).
Also, on #3 you can identify viewport sizes (for IE7 and IE8) with research. Research from the site audience, in fact. I wrote up how you can add script to your page to track viewports using Google Analytics, though it’s no good for getting data before you add the script: (...)