The Hexar is a very attractive camera. I've often thought about this question, but I'd have to sell nearly all of my cameras to buy one, so it's just a thought process now. I just enjoy shooting the Leica R glass so much that selling them isn't an option, and there's nothing that takes the place of watching the image come into focus on a good SLR viewfinder.
At this stage of the thinking I'd go for the M7 w/o any reservations. While I love the thought of motorized film advance, there's nothing like the fit and precision of a Leica camera. I once owned an M6 for a short while (decided that not having AE was too big a compromise and sold it), and it felt perfect in my hands. One thing I didn't like, having owned several M3's, is the multiple frames in the viewfinder of the M7. I don't want to see a cluttered viewfinder. The M3 has the best viewfinder I've ever seen in an RF camera. Read somewhere that you could use a little piece of tape to cover the camera's frame line illumination window and pick which frameline you want to use, so that might take care of the problem on the M7.
Other than that, the M7 and MP sound like the perfect RF cameras.