Hey Wachs! That 640 kicked ass! I was really surprised at the terrain it could handle. Don't get me wrong, there were times when I would have liked a lighter bike so that I could throw it around more. Especially in deep sand whoops. With a full almost 8 gallons of fuel that bike really liked to dig in when I let off the throttle. Of course I couldn't stay on the throttle because I was already bottoming out the suspension. The whoops I'm refering too were pretty extreme and the bike did fine with smaller sand whoops where I could stay on the throttle.
The Husqvarna 510 would have been a miserable ride on this trip. There were times when it would have been nice but overall the gearing would have had me cursing. The 610's however were very impressive as was SheepShagger's 525.