POB:

I have used a StreetPilot III for 70,000 km on a ST1100 (granted, not an off-road bike) and never had any reliability problems. The SP III is the same form factor and chassis as the III and III+ you are considering.

Leaving the reliability issue aside, the main considerations for you are processor speed and memory capacity.

Because you don't plan to use street level mapping (I am presuming you would use WorldMap cartography), I don't think processor speed is a concern. Considering that WorldMap will give you major roads only, how fast do you need to see the screen update? In my opinion, either of the 3 proposed models (III, III+, or V) would provide equal performance, even though the V does have a much faster processor.

Next consideration is the storage capacity (memory capacity) of the GPS. I'm not fully familiar with the III, but the III+ has only 1.44 megs of internal map storage. All the WorldMap segments for your proposed route (London to Jordan and back) add up to 11 megs. That means you will need to frequently reload your III+ with map data appropriate to your region - in other words, carry a portable computer. That's a PITA unless you intend to carry one in any case.

The V has 19 megs of internal memory, which is sufficient to load your entire route ahead of time. That makes it the most appropriate choice. It's also considerably smaller than the other two.

You might find it helpful to go to Garmin's website and use their "comparison" feature to compare the specifications of the three different GPS units side by side. The URL for that site is:
http://www.garmin.com/outdoor/compare.jsp

You may also want to consider the Garmin eTrex Legend GPS. This is not normally thought of as a automotive / motorcycle product, but for what your stated needs are, it would do the job. If you purchased a European unit ("Atlantic basemap"), you would get pretty much the same cartographic data as WorldMap provides, the unit is very small, lightweight, waterproof, and rugged enough, if you treat it the same way you would treat a cell phone (handy). You could probably buy one new for the same price as a used III, III+, or V. You mentioned you are already familiar with this unit, for the benefit of others, there is more information about it here:
http://www.garmin.com/products/etrexLegend/

PanEuropean

[This message has been edited by PanEuropean (edited 26 November 2003).]