I skipped the 550 and went straight from a 2820 to a 665. The reason I did it was that the weather you get on the 665 has the doppler radar map like the 475. It is really pretty cool. If you are riding around and there is rain, snow, extreme weather etc. within about 20 miles of you, it will give a alarm and a message like "Rain detected in area". You push one icon on the screen and goes to the weather screen and shows where you are in relation to the weather. If you are following a route, it will show the route on the weather map.
The larger screen is really nice, and you actually see a lot more of what is around you than the 550. It does however have one major drawback that I cannot live with. Garmin has promised to fix it, but that have not yet. Some people may not see it as a issue at all. If you download say 20 waypoints from the Mapsource software they become invisible if you zoom out to 2.0 miles or more. They only appear when you zoom in to 1.2 miles or closer. This makes it pretty worthless for using in rallies. It is really too bad because some of the other features for mapping are much better than the 2820 was. For instance if you want to add a waypoint to a route you can simply pick the point from the list, tell it to "go to" and it asks if you want to add it to the current route, or create a new one. If you choose add it to the current route, it automatically puts it in the correct spot. On the 2820 you had to open the route, choose to edit the route, choose add or edit waypoints, choose the waypoint you wanted to add, then you would have to run route optimize to get it put in the correct spot.
