I use Word 2007 and I'm considering updating to Word 2010. I'd then be using them both, depending on my needs and which version my clients give me. I may need to use Document Compare with one document created in Word 2007 and the same document edited in Word 2010. Is this possible, or must the two documents be the same version of Word?

I know you can't compare a .doc with a .docx, but what format does Word 2010 save in (.docy ;-)?