If you don't want to navigate with reference to landmarks the 500 should do fine. The 500 will take you from one GPS point to another. If you want to also be able to reference landmarks and surface features then you need something like the 705 or 800.

I have a 705 that I use on bike, car and gym. It gives me all the operating data I need and also does a very good job navigating with the maps that came with it. A very useful and comprehensive device.

My only problem has been with their customer service. But I bought from REI whose whole being is oriented around service so it has worked out