Good afternoon Jondirt,
This topic is of interest to us as well with the deployment of the new Zumo 350LM. We have both devices in the shop now and have done extensive testing in the last month on real world rides such as the Oregon Backcountry Discovery Route and regional street use. We have mounted the Zumo 350 on one bar and the Montana on the other and worked with them. The disparity is significant in multiple areas.
We have assembled our take on the new unit and have posted our findings in our GPS Ready Room thread here
. We will have the devices in the shop for another two weeks so if there are specific questions or configurations you want to look at, let us know and we can sample them for you. We too have looked at all of the considerations that you have listed in addition to our own and have decided on the core devices to use.
Based on our testing, at this time, the Garmin Zumo 66x and Montana 6xx are the two series PND's that are recommended for your specific needs. The Zumo 350LM is a mild replacement for the Zumo 550 and lacks some inherent and important off road capabilites that will take extensive O.S. service packs to overcome, if at all.
Thumbs up - Dan Townsley is a respected GPS user and has real world experience in global travel with various GPS' under commercial use and environments. Glad he provided his input here.
Good luck with your decision. BTW, we like the TAT too.....
River Pilot Tours
Cheyenne, WY. U.S.A.
PH: (01) 307-222-6347