At the end of the day, you need to decide what is comfortable for YOU.
I don't think you should exceed your payload rating of your truck. That is the first step, making sure that your loaded trailer attached to your loaded tow vehicle with a PROPERLY SET UP WDH are weighed and your numbers meet Toyota's specs.
Once you have made sure that you meet Toyota's specs and are at or below your maximum weight rating, you need to feel comfortable driving it. There is no chart or ratings to determine this... you have to know if you feel comfortable towing this weight.
Those are the two variables to know if you are towing too much weight or if you are light enough.
