Sometimes a 10x5 adds that little extra sparkle that helps some trainers flying off of rough grass fields get airborne sooner.
Actually, it was a rough grass field that convinced me go to with the 11x5 on my SPAD Debonair trainer when I had the LA 46 on the nose. The 10x6 and 10x7 would pull it off, but the 11x5 made approaches easier and takeoffs quicker with the addtional thrust.
Brad