There seems to be a trend when reading a lot of the threads having to do with headers people talk about the different types and different manufactures. Recently it seems that a large group of people are having problems with the manifold bolts breaking and people seem to be wanting to replace the stock manifolds with "shorties", due to the cost and secondarily the gains in performance, however small that gain might be. The other group of guys, I believe are really interested in performance gains and that is why they are drawn to the long tube headers, which in many cases cost considerably more, but the performance gains are greater than the "shorties". I don't personally have the dyno charts to prove that there is a considerable increased gain in performance however they do exist and have been posted before. Keeping in mind that to realize the full performance gain you must have a tuner and your truck needs to be tuned with the headers. Some of the loss in torque you talk about is in direct proportion to the headers tube size. Most people that believe they have lost a considerable amount of torque compensate by purchasing a high stall converter. I think that Matt at Moe's Performance has copies of the dyno charts you want to see, you might contact him if your interested.
Jay