Never put a GPS on mine.......what passes for planning on that hull style varies load to load and I only very rarely used it for really long runs.....most times I was towing a decoy sled and dealing with a swell or heavy chop so the advantages of the hull as a heavy water performer was far more important than speed.........
I was always loaded down with Fat Men and Iron, and a dog, cork decoys, and too much "stuff", and thinking about it now in all the years I've had them and run them I don't think I ever ran one of them "empty".....no doubt a much quicker and more nimble boat in that load out....
Steve