A good place to learn all about Garmin M/C GPS's.
I have a Zumo 660. It is a little pricey, but is has several big pluses.
It streams stereo Bluetooth. Think of the device as a GPS, phone, and stereo. A2DP makes a big difference. Paired with a decent A2DP Stereo Bluetooth helmet speakerset like Chatterbox, Sena or Scala, makes for a great touring experiencel. It pairs up to your phone and will give call display and phone book onscreen. It holds a micro SD card so you can have the entire North American continent and around 1000+ songs all on one device. If you buy two Bluetooth helmet sets, you can use them as a rider to rider or pillion intercom, while still getting full GPS directions as it prioritizes channels. GPS, intercom, phone, music. The screen size is good and easily readable in direct sunlight. The screen works well with gloves on as well, while many car GPS unit won't.
I used the included ram mount using the screws from my clutch bar clamp. Install was easy and I only needed to remove one side of the fairing. Its wired onto the battery with a line fuse. The car kit was included as well so the unit gets good use.
The minus for the Zumo 660, (besides price), is that when first released the firmware was quite buggy. There have been numerous firmware updates to address this, but I would be reluctant to be a launch customer with any new Garmin product in the future. (My wife gave this to me as a birthday gift weeks after it came to market.)
In the end you pay more, and you get more. For multi day touring, I wouldn't trade my zumo for a car based gps.