You've hit on two of the four biggest differences - the other two being that the 550 speaks the street names for the upcoming turns and comes with the automotive mount and power cable (as well as an AC adapter, but many never use that anyway).
The car cradle and power cable will cost you about $100 if you want to use it in the car without pulling the cradle off your bike.
You can use the M C mount between a M C and car and do not need a second mount.
I used the MC cradle, had a suction cup mount, made a power cord to plug into the cigarette lighter and bought a cassette adapter to get the MP3 and GPS prompts through the truck speakers. If you don't have a cassette player in the vehicle you could use a FM modulator. Note the inline connector on the power supply. Makes for a quick swap between bike and truck. On the bike
Garmin is discontinuing the 450 model and replacing with a 660 model. You might wait a few weeks and find the 450 heavily discounted, as vendors are going to try and sell off their stock.
I agree with John. Unless you can find a 450 at a blowout price, I would wait for the 660. The 660 looks like a real nice unit, and less cost than a 550, with a bigger display in smaller size case.
A forum community dedicated to Honda Goldwing owners and enthusiasts. Come join the discussion about performance, modifications, touring, troubleshooting, maintenance, and more!