I've been using IE Tester (good) but didn't know I could simply switch versions in IE. It's nice to know the browser voted "Most likely to be the bain of your existence" has the tool built in to look at previous versions.
The down side to IE Tester is it does not support javascript well, and also doesn't always do a great job with iframes. (Yes, I still use them.)
I decided that since Google and Facebook no longer support IE7, I won't either. I have a lot less funding than they do.
I know this doesn't fix the need to use VM for MAC users, but there should be ways around that too. With an 8 core processor PC computer, you can VM MAC with 4 cores, same for PC, and run 4 displays, two for each OS. Expensive, but this is our business. In most business models, it is not uncommon to spend tens of thousands of dollars on equipment. We shouldn't think of ourselves any differently. Invest in your success.