I guess you are interested in the twins/triple
Well Dan, no one has owned up, so far, to riding all of those bikes offroad.
I have ridden one or two of them onroad only and I would say the Wee strom is as good as any of them, and better than most, on the basis of weight alone; as mentioned before, tyres come into the equation a little bit
If you do a search for Mollydogs' posts he has said quite a bit about the bigger DL1000 capabilities offroad and he reckons that the Wee Strom is just as good, if not better, again because of the weight.
Finally, as ever, what you mean by offroad is not necessarily what another rider means!!