Hmmm... you joined 4 years ago. I suspect you know already there is far from any consensus.
Cargo capacity is generally speaking the least forgiving number and the one that is generally reached or exceeded first.
Length - there are some recommended formula's out there that take into consideration a tow vehicle's wheelspan, but that's even subjective.
I have a 40 ft 5th wheel I pull with a one ton SRW. Im within all my weight capacities and have no issues towing it.
Mike