Wren, you might want to pick up several of the black cox props. Maybe a 5x3,6x3, and a 7x3. Try them all. I found the 5x3 to give the best speed, so step up for lower speed and rpm and slightly higher thrust I keep saying to get the cox props because I've had very good success with them. Heck, I even use them on my Norvels! (BLASPHEMY!!!)
Fine tuning your setup takes time and is rewarding.