The 640 ADV is very well sought after and very scarce. Not too many people know about them and not too many available in the US. A well established KTM dealership may get ONE allotment and that's it.
It's a lot lighter than the 950 ADV, alas it's also a lot taller (37" inseam). Down on power for highway cruising. With a regular guy and cargo, it would be hard pressed to hit 75-MPH. So if you plan on riding the interstates to get to where you're going to do some adventure riding then beware of the lack in passing power or bucking headwind not to mention at top RPM the thumper will vibrate like crazy. If you don't plan on riding the interstates then it's cool.