Can't get more clear than this:
Ford Towing Guide wrote:
Trailer tongue (trailer king pin for 5th-wheel towing) load weight should be 10-15% (15-25% for 5th-wheel towing) of total loaded trailer weight. Make sure vehicle payload (reduce by option weight) will accommodate trailer tongue (trailer king pin for 5th-wheel towing) load weight and weight of passengers and cargo added to towing vehicle. Addition of trailer tongue (trailer king pin for 5th-wheel towing) load weight and weight of passengers and cargo must not cause vehicle weights to exceed rear GAWR or GVWR. These ratings can be found on the vehicle Safety Compliance Certification Label.
So that means the lowest of your specific truck/trailer combo rating should not be exceeded according to your vehicle manufacturer. Many people exceed one or more of their ratings to varied real world performance. Only you can choose to follow the manufacturer specs and if not, which ones are "important".
