I fly a Mojo 60 with a Saito 91, 14x6 or 15x4w. The 91 is plenty for a 5 1/2 lb plane for me. I have a Mojo 40 with an OS 50, 12.25x3.75 prop. I have a Saito 100 on a Razoryak, 15x6 prop. And a Saito 125 on a 8 lb Mojo 65, 16x6 prop. I have never felt the need for more engine on any of these planes with the Saitos. The Mojo 40 with the OS 50 feels a little weak sometimes. My next project will be a Mojo 60 with the Moass mod.