As I always suggest , I take a handful of props in the appropriate range and test fly them to see which one flys the plane the best. I think you should mount the 12X10 and get a tach reading to establish a baseline. I would be interested to know what the 61 Is and what tach reading you were getting that it didn't work on your setup. I use an 11X7 on my Enya 60X with great results.