You know what...... I would be very wary of taking loading to the line just because you have one aircraft that has a slightly different MAUW to another. Not to mention that I will bet you a months supply of beer that if you weighed the aircraft prior to flight you find the actual weight very different from the load sheet unless the aicraft had a weight and balance done the day before. Most W&B sheets are way out of date and without exception every aircraft goes up in weight every time it is weighed. Fabrics take on moisture etc.
Just because you have a higher MTOW does not mean you have any extra performance.
A wise man gives himself a good margin for error..................
I personally will not fly any Cherokee 4 up regardless of the fuel load and with a Warrior I would be looking at around 2 hrs fuel.
As a point the Cherokee I teach in has a placard for the maximum weight on the rear seat of around 180lbs(I will go and check the exact figure in a bit).
If you want to carry more passengers get a more powerful aircraft, not put other peoples lives at risk with creative accounting.......