100 feet of ladder line is sort of a magic number for being easily tunable on all the bands. One of my friends bought a ready-made 80M dipole with 100 feet of ladder line and a tuner; and the instructions were not to cut much if any off the ladder line. I learned the reason for that later when I ran across a web page (which I can't find right now) where the guy has a similar antenna that he tunes by inserting various lengths of feedline. He has a graph showing that 100 feet comes pretty close to being a good match on all the ham bands.
Here it is http://www.w5dxp.com/notuner.htm
