I have a little experience with running props on an OS .46 DF. I tried several different odd ball APC sizes and I ended up liking the 7.8 x 7 APC pylon prop. It has been several years since I had this combo. I don't remember what RPM it was turning (I think it was around 22K-23K on the ground), but it worked out well. I was running a Macs pipe, but I don't remember what the part # was. Hope this helps.