I'm quite interested in this topic. Here in the Netherlands we have to get our towing weights registered on the registration papers of the car.
Rigt now I have 0 kg braked and unbraked.
However I have towed a trailer of which I think was about 1800 kg up the steep hills in the belgium ardennes without any problem.
Official weights would make it much easier and cheaper to get my towing weights registered. So I can legally tow my trailers.
Without official numbers I probably need to get it tested on a test track. Hope to get around 1800 kg or 2000 kg for a braked trailer.