Belts are quieter, cleaner but less user friendly for me - never had a belt go on me whilst out on the H-D in many, many miles but they give no indication of wear in the same way as a chain does.
I think if I were to tune or get serious with the M3W (i.e. pay the bills out of warranty..) I'd be inclined towards an enclosed chain, and put up with any increased noise in exchange for ease of maintenance and the ability to adapt gearing a lot easier.
Automatic chain oilers are cheap and effective, and enclosure prevents the biggest chain killers of grit and water.
My mind would be to develop belt alternatives rather than chase ever decreasing suppliers of specialist belt sprockets with unique specification issues.
