The 58/115/116 all have looong exhaust durations. It doesn't hurt to start long and work your way back. I would recommend doing this on a test stand, because it is a b$tch doing it in a plane. If you do the math the length from the piston face to reflector cone is almost prohibitive in our model airplanes and that is from Mr. engine himself Gordon Jennings.
The 116 is just two 58 cylinders put together, if one likes higher rpm so will the other. Shoot for mid 6's to 7's on the 115/116.