The tow bars that are available are all Class 1, rated for 1000 pounds. My trailer is 375lbs, with a 550 bike on it were over 900. Drives fine, and didnt have any issues passing cars going up the mountain to the parkway.
I add that I have bigger audi brakes up front for the down hill side.
I have towed quite a bit w/ NBs, both a 2.0L and a 1.8T. For some reason we do not get towing info in the USA. However, years ago there was discussion here w/ someone from Australia and some in Europe where it appears they got numbers in their manuals up to about 2000lbs. My personal experience is that much over 1000lbs. really effects the handling and braking of the vehicle and I would not personally recommend much more than that.