Hi Wolfau,
I have been working with a Garmin Montana 650T with the Aust NZ topo map V4 for the past ten months or so,very happy with it.
The 650T has a big screen that is easily read in bright sunlight, also when it's installed in the auto mount (recommended) it's great for in-car navigation both in the bush and as a street navigator with audio prompts; IE both in-car and a hand-held unit in the one device.
With Garmin's Basecamp software (free download) you can do a lot of planing at home on a desktop or laptop on areas you intend to prospect; just connect the 650T to the computer and the topo map will come up on Basecamp, you can create waypoints, tracks and routes and then up-load them to the GPS.
Google Garmin and you will find a stack of info on their range of GPS units and some great video tutorials.
The only downside is they cost around $7oo.oo with the topo V4 map and auto kit, also they are larger and a bit heavier than the others in the range, that said though they are a fab unit and in my opinion well worth the $$$$$s and the heavier weight given the features.
Hope the above is of some help.
Cheers,SinHof.