Just managed to get my hands on one, very cool!
I have a 300, it seems that the only difference between the 300 and 400 series is the maps with which they are packaged (the 300 doesn't come with any maps in the box, only trip and waypoint manager)
Here's a comparison of the features:
https://buy.garmin.com/shop/compare....ompare=compare
Looking at the unit, I can see that you're right, there are a LOT of features, I'm going to need to time to think about this :-)
David