I have the WM GS mustang with a Moki 210, probally pretty similar performace. This will be my season # 3 with the plane. I have found the APC 18x12 prop to be the best combo for my mustang, lots of speed and great thrust. One warning, If you are flying on a calm day I would suggest landing with flaps and dail in about 6% down elevator with them, my first landing was without flaps and the mustang did a sudden snap about 1 ft off of the ground without warning at all, since then I have always used flaps for landings and have not had the plane snap on me again. Other than that if you fly off of a grass runway you may want to hold down a little more up elevator than normal, seems mine will like to tip over in the grass fairly easily with the stock gear, sometimes it seems that it lifts off a little too early while holding in the down elevator but the moki has enough power to overcome an underspeed takeoff.
Best of Luck let us know how it comes out.

Michael