There are bike mounts available for hand held units and many hand helds do a good job at automotive navigation and a great job geocaching. On the other hand most automotive units (like the ones you linked) to are not particularly good for geocaching, they are designed for automotive use.
A Garmin Map 60CSX, Oregin, Vista HCX or Legend HCX will do a fine job of navigating roads if you also spring for the City Navigator software.
Delorme PN40 and PN60 aren't nearly as good as the Garmin unit for road navigation, but they do have rudimentary navigation features and are excellent geocaching units.
There also are the Garmin Nuvi 500 and 550. These are automotive units that are ruggedized, water resistant and designed for outdoor use and have the geocaching friendly features that most other automotive units lack.
Another thing to consider with automotive units on you motorbike is that most are not water resistant. So if you run into a rain storm you will need to somehow protect the unit.
Thank you Briansnat,
Of all these, I prefer the Garmin Nuvi 550, it is the one nearest to what I need, it will have the possibility to connect ear-phones, is water and vibration proof and hopefully a power connector for the motorbike battery.
While rading about the above GPS, I came across these:
The GARMIN - DAKOTA 20 looks nice too. The Garmin Oregon 400T has topographic maps included, but I could not find about navigating on roads/cities (oh, it might be discontinued). Buyt these two have a quite small screen.
Is it possible to add topographic maps on any GPS?
Thanks,
Yoram