I've raced, nationally and internationally, for years, driven fast for long stretches of time on autoroutes, etc, but I would never underestimate the effect of 2.5 - 3 tons of mass, a high CoG, touring rubber, road conditions, my own tiredness, traffic and 'the other idiot' on my ability to keep my family & I out of harms way while driving.
Just because these vans feel stable at 100+mph while in a straight line does not mean they will behave nicely if a sudden swerve is required or hard braking on an uneven surface. And if it all goes pete tong then that's a lot of blood on my hands.
That said, there are times when it makes sense to up the pace a little, assuming conditions allow. This is rare in the UK but very common across much of the continent, and the fines link above clearly demonstrates where the perceived risk thresholds are.
I look forward to finding out what's safe & reasonable when I first hit the autobahns with the T6, but I'll do my fact finding without the family in the car, in good conditions and with a wide margin of error!