Just checked and the steepest trailering we did with the Tornado behind Focus was 10% climbs. Speed limit was 80km/h and we could follow the traffic by gearing down.
Towing a tilt trailer is usually murder for the mpg if you go long/fast <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> By breaking the Tornado down we could tow the hulls in the wake behind the car, but the mast poking up and forward over the car still made for some drag.
I find driving a largish car is much more comfortable when driving on highways for 6-xx hours. But money is what decides in the end.

Mike trailered his T from Calif to FL, but not behind the Mini and not in tilt mode (I think). He should be able to share some good information next time he checks in here.