I'm happy with my 22' 14K PJ full tilt trailer. I agree that you may want to go longer. I went from a 20' to 22' when I upgraded trailers.
I'm still trying to figure out the whole trailer length thing.. I have a 22' ramp trailer and a 20' full tilt. .. the full tilt is a 10k the 22 is 17.5k .. the problem is that the longer trailer is so heavy to begin with, even empty is makes the read of my F350 squat.. load it up and the front is 5" higher than the back of the truck. I know it has to do with wheel position on the trailer.. but inevitably the longer it is.. the further back the wheels are.. the more weight on the hitch...