Haven't ridden one, but I;d bet it's probably not much more
comfortable for the passenger than the 640. I took a good look at the
seat on the XC at Custom Cycle yesterday, and it's nothing terribly
special. If you want passenger comfort you might have to get a 1200GS
or something like that. But to be honest, I haven't found a seat that
didn't hurt my a$$ after a few hours of steady riding. When I got
back from our Manitoba TCAT ride it was a week before I could sit down
without feeling any pain (I rode my '07 KLR on that trip - 2750 km
over 5 days).
Whatever you decide, good luck. The XC is a pretty nice bike, though
the BMW F800GS is supposed to be a bit better off-road.
Chris
2007 KLR 650
2000 XR650R
2007 Versys