The Maxi Marine rubber also has a 3 position micro-adjustment you can make. You should probably size it big (err on the big side), and if need be, micro-adjust smaller.
Cutting it. Some people mouse around with a razor blade. When I cut these style straps, I use a "professional" Chef or Sushi knife in one press downward guillotine style (hand on handle and hand on top of blade for consistent leverage). The weight and sharpness makes for a quick/clean cut. I stress professional knife. This is similar to what I used on my Ocean Racer (same concept).
If you screw it up, let me know, I have a "Bracelet" if you want to ditch the rubber.