450Nm is plenty for float towing. No need for 550Nm. I have towed a four horse float loaded with 3 large Irish sport horses with no problems behind mine. With the larger weights nearer to 3.5 ton the stopping is going to be the issue and not getting up and going. You don't need really need any more grunt than the 450, because there is no need to launch rapidly with horses aboard. Will merrily haul things along at the speed limit comfortably. As it happened when I towed the 4 horse float, it was only after driving quite a few KMs I realised the electric brakes in the float were unserviceable and the car was doing all the stopping. Not the best situation to be in but the Touareg was stopping the whole combo without any problem. So I continued to destination a couple of hundred kms away.
The only downside to the lack of air suspension is the basic system is not self leveling. So the Touareg will sit down in the rear somewhat. To me this is purely a visual issue as it does not seem to effect performance in any way. The suspension never bottoms out.
Also have a 10 ton, 4 horse truck and the one thing that stands out is with the Touareg (or any modern car) - it is very easy to merrily belt along a 100-110kmh without much thought about how to stop the whole deal in an emergency. In the old Truck it is an effort to get up to these speeds and I tend to cruise ~ 20kph slower. There is an illusion of safety, possibly due to how easily the Touareg tows..