Good afternoon Tom (Rider351),
Excellent question and a common one. Both the Garmin Zumo 660/665LM and Garmin Montana 66x are excellent platforms. Advice about these specific devices can be found on the ADV Rider forum here
in the "GPS Ready Room". You can also find information about how they interact with routes, tracks, map creation software and external mapping product cards there.
Both will serve you well and are perfect for your bike. Both handle routes and tracks with ease and are easy to read. You will be happy with the upgrade in either instance. Since you are splitting your riding, the bluetooth on the Zumo 660/665LM will be a nice addition and the Zumo model lines come with the fuel management dashboard.
Given that you have the BMW R1200, you would want to look at the stock BMW Navigator IV. Specs on that device can be found directly on Garmins website here
. The device can be purchased directly from your authorized BMW motorcycle dealer or an authorized Garmin dealer. Price will be $899.00. For that price, you receive the custom cradle for the R1200 and its generally designed for that bike model range. Durability is not an issue.
The Garmin Zumo 660/665 and the Navigator IV are the same platforms but the Nav IV is made for BMW as an OEM product.
If you want to save some money by not having the custom BMW cradle and buttons, the Zumo 660/665LM will be the next best selection.
If you believe that you will do more off road riding than anything else, then the Garmin Montana 66x is definitely the best solution. Ensure that you purchase the City Navigator North America 2013.3 map with it so you can use it as a street device. You'll need the corresponding AMPS mount and RAM handlebar kit to mount it to your bike. You'll also want to buy a screen protector from Zagg (modify it for the Montana by trimming) or the OEM covers from Garmin. The Zagg is clearer but the Montana OEM comes in a three pack and is acceptable. Cost negligible.
Both devices will handle your 24k topo card that is routable. You can look at additional cards here
Good luck with your selection.
River Pilot Tours
Cheyenne, WY. U.S.A.
PH: (01) 307-222-6347