Uh... I believe we found the Megan coilover kit has LESS clearance than the stock strut. I recall the thread where this was discussed, and it was about 1/8" less clearance.
Frozen, a 10" wide isn't going to work without pulling the fender and still poking. At least in the front. But you can definitely do it in the back, and I would. A staggered fitment is great on these cars provided you pay attention to tire circumference. 245/45-20 front, 275/40-20 rear, and you're golden. Some even roll a 255/45-20 front and do OK. But the rear flanks are wider than the front, so this staggered fitment covers a nice flush look front to back. Same for the Flex, almost exactly.
edit:
Here is some more info to mull over
http://www.hrsprings.com/projects/detail/hr-ford-taurus-sho/That's the H&R SHO. Used to run a staggered 22x9 (with the rear just having more offset.) Runs a 265/35-22, front and rear. Their new setup is back down to 20", like you're thinking. But it is staggered 20x9 and 20x10, 255/45 and 275/40. As you can see by the fitment, this is the limit just about, before you start to do fender pulling and other more drastic things.
Notice the 20x9 and 22x9 front fit in these pics. An extra inch is not possible, without A: doing a stretch fitment and pulling the fender, or B: just ignoring that and poking out, hell with the rest.
Also notice how badass awesome the rear looks filled out like it does. I personally would have just kept the 22's, but they were going for the lighter, more racy appearance on the BBS units, so +1 for that I guess. 21" would have been perfect too.