The DD setup from Southbend is top notch. However, noise, pedal pressure, and drivability become more of an issue. I would say how much more do you want to take your truck? Right now, a Single disc will suffice for you. And the pedal pressure is butter smooth, no extra noise, and cost 1/2 the price.
If you are going to constantly be working your truck, pulling, or dragging then the DD becomes more of a player.
i just went through this and think i caught you on the DTR site about the drags... . Not very nice on clutches, I have seen more than one smoked. I just recently installed a SBC DD and have had possibly some issues. Peter at SBC has been great, they really stand behind their work. They have sent a second up to replace the first. I was getting some fairly loud rattle, and the truck's throw out bearing was making some wierd noises. So, out with the first and in with the second. i plan on updating how it goes... .
As for you let us know what you decide.