I have an OS 1.20 four stroke on my TF Cessna. You are correct that full power is only needed on take off - then back to maybe 1/3 rd. I use a 3-blade Master Airscrew 14 x 8 and get about 10,000 rpm at full throttle. I also have a Gropner 14 x 8 but it does not fit in the spinner.