Exceeding the 85% recommended limit

I am new to caravaning and need some advice from fellow tourers out there before I commit to buying.

I own a Ford Mondeo 2.0 TDCi (140bhp). I am after a 6 berth (new) and haveven looking at the Baileys Ancona, Swift Major 6 as well as one or two others. The MPTLM of these vans is just shy of 1,500kg and the car's kerb weight is 1,537kg.

The caravan club recommend not exceeding 85%, but it's almost impossible to find a 6 berth fitting this ratio. The dealer say I can legally tow 1,800kg in my car. I wouldn't want to go this high but why is it recommended 85% of kerb weight not maximum tow weight?

Also, there are safety devices that can prevent snaking these days so can these be factored in?

I'm completely confused but would like to know opinions on towing 90-95% of kerb weight.