I would run a 20x10 the moki has a lot of torque and is better suited to run at lower rpms. I don't think the 20x8 would take advantage of the torque curve of the big moki. You may also want to try a 22x8 prop. Right now I do not have the moki in my 3d plane but I can tell you that with about 1 gallon of fuel through mine and running it pretty rich it's turning an APC 18x14 prop at about 7200 rpm. I use power master 5% fuel which is the most moki recommends, it will be hard to hold a constant needle setting a void the warranty with higer nitro's, there simply no need.