After deciding to upgrade from a smaller unit, I decided on the Garmin Montana 600.
I also got a AMPS Rugged Mount that fits it (there is one with and one without electrical connections). Decided on the cheaper one that comes without electrical wires. The Montana 600 can go 16 hours on it's own Li-Ion battery or 22 hours on 3 AAA's. I intend fitting a USB socket on the Tenere for charging the unit.
The connection between the top bar and the AMPS Mount is a GPS handlebar mount with a rubber spacer to fit around the thin top bar.



This is what the setup with the Montana 600 looks like. I have the South African as well as the Australian Topo maps on it and have used it in both countries

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2014 XT660Z - Barrett pipe, DNA stage1.5, Barkbuster hand guards and handlebars, Pivot pegs, Teknik suspension, Guard-it engine protector combo, B&B rear rack, Trax topbox.