I have a hard time believing that a Sorento will pull 5k with any adequacy. My trailer weighs 5k, with a 650 pound tounge. I've moved it a few times with my Nissan Fronier, I thought that thing was going to hit the ground lol.
Anyway, maybe a 5k boat with 8% tounge weight and no frontal area. But I don't believe a 5k TT will be acceptable.
But I'm old and like steel frames and V8's.
Btw, what kind of mileage will a V6 Sorento get? I bet it's not much better than a larger SUV (or, god forbid, a nice full size van :B )
To answer your very original question, a tow vehicle with a higher tow rating will tow better and handle better than a tow vehicle with a lower tow rating while towing the same trailer, even if that trailer is at/below both tow vehicles ratings.