who went from a garmin 478 to montana 650 need input

As long as you load auto-routing maps, the Montana will auto-route.

And you'd be able to listen to XM through a phone or dedicated device.

Yeah, that's what I did before and had an XM Roady receiver and used a little Garmin Etrex on my F650. The great thing about the 376C is that the XM is a part of the GPS, so I only have the one device on my bars. I'm real attached to the 376C, have the Touratech locking holder, hard wired in... you know, perfect. Love the variety of XM on a long road trip, not a fan of the short battery life of smart phones or iPods, though I could wire a feed into the tank bag I suppose and bluetooth the sounds to some earphones.

I can understand the reluctance to get away from something you have so much invested in...

But as far as having just one device on the bars, I prefer to spread things out a little so if something dies or gets stolen, then not everything I enjoy or depend on goes with it.

Well, technically you have two devices with that big ole hockey puck receiver connected to your 376.

Why the Montana over the Zumo 660/665?

The Montana is much more versatile. That may be why BMW chose it as their gps of choice for the BMW GS Trophy Challenge.

"Another new partner is Garmin, which is providing a world premiere for the GS Trophy: the brand new BMW Motorrad Adventure navigation system, which is based on the Garmin Montana. We are using the very first units of the Adventure. It will be available next year."

I was advised by the "X sperts" the Montana would better fit my riding. I hooked the Montana up on my bike and rode home 1500 miles mad at that "Xspert". I expected a zumo type machine just tougher. I ride lots of off the beaten path, dirt tracks and definitely not interstate. It does that quite well. Montana accepts my old topo maps for back woods navigation and lets me switch views from street maps to topo easily. Its not a Zumo but it will navigate like one. It dosent talk to you, play XM or link to your phone. But then the reason I ride the back roads is to enjoy being off the net. Bought the Montana and tried it. Know what? They were right and I like the Montana better. It still don't talk, answer the phone or play music via blue tooth but I enjoy the solitude of the ride much more. I put the Zumo in my pickup truck.

So the Montana's don't do "voice" turn by turn directions? If so I'm out.. That is a feature that I really like... I still ride alot of slab..

The Montana does have voice directions with the right maps and the right mount. If you use the Rugged Mount as most people do, it has an audio cable out which you can plug into your headset of choice. It doesn't have Bluetooth for wireless communication, but the audio output can be hooked up to a BT dongle if you must have that.