I own a Quigley, and I have driven my brother's Quadvan quite a bit. Both can handle significant 4wd challenges. See viewtopic.php?f=11&t=4819
for example. My brother's Quadvan handles significantly better than my Quigley. The larger front brake rotors help, too. On the downside, the 2" lift on the Quadvan really is not enough and his stock Ford rear leafs with helper springs are super rigid compared with the Deavers that are on my Quigley. FWIW, my recommendation is Quadvan with 4" lift and Deaver rear springs. But I'd be pretty happy with SMB 4WD if I had the chance.