I appreciate that going well over the 85% figure worked for Jezzer B, but as someone who investigated accidents I cannot get anywhere near suggesting you exceed the kerb weight of the car. It might work with some combinations, but it is a significant risk, as you cannot be sure how well the combination works before you buy, so caution has to be the watchword.
I do accept that the 85% figure is probably a bit low with the advances in both car and caravan suspensions, plus other safety features, but for a beginner I would be reluctant to go anything significantly over 90%.
The recommendation is there for the safety of people new to towing caravans, basically you exceed it at your own risk.