If your ground will allow you to run a 20' (not too hilly/rolling) you definitely want to. I ran a 15 for years in beans and never could get a clean sample. Bought an old 20' head and my problems went away. You will have no trouble with the combine handling it. I have a 93 R52 with the small shoe and 180hp Deutz and can easily run along 5mph in 65bpa beans. Haven't grown any wheat in many years but had 100 acres of oats a few year ago and it seems to me about 3 - 4 mph range for them and we cut them short for the straw. Handles rye fairly well, as we grow a few acres for seed/fall ground cover. I have been told that the cummins engine uses a little more fuel but you get more hp too.