I got on one of the divide trails on one of my first times riding dirt bikes on an xr600.
Scared the shit out of me due to the high negative consequence of failing off of a cliff.. I'm (probably..) a better rider now, but even more conservative. I'll probably never ride those trails again it because the cliffs spooked me so much. I really don't want to end up at the bottom of a ravine. I recall the trail being very narrow.
On a 640?, the ride to the Sierra Buttes lookout tower ride is perfect, beautiful and fun. I've heard the road to Poker Flat and LaPorte is great for small dual sports, never been on it yet. I have been to Saddleback lookout, it is also awesome. I've done both lookouts (not poker flat road) in a Honda Ridgeline and the Sierra Buttes lookout on an XR650r. So a 640 with bags should be fine.
a thread I found