David,
The choice is always one point to start in the world of our job or passion.
I use Leica M6, because I liked to use one completely mecanical camera. You decide about what you want, without surprise of the electronic and some decision. I travel with two M6, and the 21/2.8, the 35/2.0, and the 75/1.4
To decide to have all of this I had to spend a lot of time. I'm sure that we can decide without to think about price or weight or other detail, but when we need one kind of lens it happends not only one time but everytime. We need to satisfy our eyes or mind, because it is our view of reality that make the decision, nothing else. But for this we need to take time and to see which kind of view we always need in our adventure in potography.
About XPan, the difference is that it is one completely automatic camera, without autofucus. The problem is that if you don't have battery you can turn at home, and the battery fall down in only few seconds, you don't have time to take one more picture.
But what you have with the panoramic camera, is very exceptional.
The viewfinder is better than the LeicaM, and when you use the tele the view is adjusted, bigger.
I find the handling of the XPan good enough. With the M6, I need to use the handgrip, and with this it is better than the Xpan.
Make the good choice.
Regards
Laurent