The shoulder rigs I like were shown in the movie "Exposure". If I ever got one I was going play the movie, stop it a few times in appropriate spots, take a few pictures of the screen with my digital camera, print them out and take them to the leathersmith. That way I could show him exactly what I wanted and could also get a measured custom fit. The rigs in the movie looked comfortable and quiet (made from leather) and were designed for a quick "down-pull" of a medium to large fixed blade. If you are interested, the movie is available, used, on Amazon in VHS format (not made anymore). Plus, you have a great movie to see with the best knife work of any movie there is.
Regards