My Bob Jackson World Tour is made from Reynolds 631, but it is a special tubeset designed for touring bikes. It has thicker walls and perhaps butting than regular 631. I'm not sure if regular 631 would have any advantages over any other tubing. I have another bike (Gunnar Crosshairs) made from Reynolds 853. It feels lighter than the BJ, but I haven't actually weighed the two bikes set up comparably. I haven't ridden the Gunnar on a tour so I don't know how it would handle fully loaded, but I use it for commuting and have carried moderate loads plenty of times. The Bob Jackson is definitely a stiffer riding frame unloaded, and for that reason (in part), I run 32 mm tires on it. The frame is a little too stiff for my preferences riding unloaded on 28 mm or narrower tires. The Gunnar, in contrast, rides very nice on 25-28 mm tires.