I asked essentially the same question to several different guys at work who tow trailers nearly every weekend for their race teams. What they all told me is that tow rating of a vehicle has nothing to do with moving the load forward. Its all based on getting it to stop. They also said that it has nothing to do with how fast you'll be able to go when pulling the load--that yes, you could tow the max rated load, but just don't expect to go as fast as you would with a lesser load.