Hey Colorado,
I used to live outside C. Springs, and so I can kind of imagine your situation. I don't have a lot of experience with this unit yet on very rugged terrain, but I can say that I've jumped it and its gotten rained on a couple of times without so much as a burp. But here's what I think is the deal. The mount that comes with the Zumo is totally solid. I didn't have a lot of confidence in that fact then I bought mine, but they cut some slots into the inner section of the u-bolt, where it contacts the bar, that keeps it from slipping under heavy bouncing. After a number of jumps my GPS sits right where I told it to. I've looked at the handlebar mount for the Montana, and it looks pretty good, but I think the mount for the Zumo is better for rough terrain. The Zumo mount locks your unit into the mount where the Montana mount just clips your $500 computer into plastic. Otherwise, the Montana is just as good as a Zumo, if not cooler with its camera and all. But if I wanted to drop a bike from 500 feet in the air to the ground (lets hope not) then I'd put my money on the Zumo mount.
Later
Bartlioni