Hi, we have just returned from a week away towing our 20', twin axle Lunar 615 1400kg mtplm with our s-max 2.0tdi, there was never any hint of instability cruising at 60mph, occasionally hitting 70, We chose the S-max over the Galaxy for cost and style and we did not need the slightly larger load space. Although my knees are very bent in the rear seats there is actually more headroom than in our old Sharan despite what some reports say. I have reported in other threads that the S-max is actually more economical in 5th rather than 6th gear solo, 4th is more economical than 5th when towing, ie the six speed box is a waste of time.
MPG solo
54 @ 55mph in 6th
60 @ 55mph in 5th
37 @ 80mph in 6th
39.5 @ 80mph in 6th
MPG towing
27 @ 60mph in 5th
29 @ 60 mph in 4th
all figures gained using cruise control