One thing I don't understand:
1. You say you MUST sell the Pro TL.
2. But you are OK trading it for an M3.
Why do you have to sell the second Mamiya? That I do not understand. A back-up body and lenses is invaluable to have.
I love my Leica. And I love my Pentax KX SLR equally. The 'Leica thing' wears off pretty quickly, and it becomes a reliable box that holds film. In the end, it's the pictures that matter. If you think you can make better pictures with the Leica, then go for it. If not, then why not keep what you've already got? You're just making it more complicated with two different formats and cameras. What purpose does it serve?