I have some great news. I have been trying out the larger props more extensively and have found the 11X7 to work quite well at less than full throttle. My biggest problem has been fighting wind so I have been more patient and waited until later in the day so I don't need full throttle . Next I am looking into Nimh batteries, I have been using 9.6V AA size Nicds and they seem rather heavy but it is working OK( I considered it a challenge). It has been a lot of fun developing my plane to fly a cheap as humanly possible.
I plan to go full boogie on the next level plane, a GWS Corsair using the lightest and most powerful components I can afford. I would love to use a 3 bladed prop to make it look scale but that will be up for further discussion when the time comes.