Most .61's do very well with a 12X6, a 13X6 is a bit much. It won't spool up very fast and may overload the engine. You may want to look at the tower web site and see what props are recommended of other .61 two strokes like magnums, thunder tiger, super tigre and so on. I have several .61's, .75's and so on. the .61's really pull strong with an APC 12X6. The .75's do okay with a 13X6, but really scream on a 12X6. If your into slow and steady a 13X4 APC wide works well with a .61. Your engine may even be strong enough for a 14X4. If you have a need for speed, the 11X7 will make it fast, but doesn't slow down well for easy landings. Hope this helps.