RE: DDust pulling hard to the right.
I would hazard a guess that the prop doesn't have much to do with it. Slow take off speed caused me a right roll/smack down but that was with a small plane (not a delta) and it was probably a low speed stall.
My ddust with a 46fx and 9x9 is somewhat slow off the mark but tracks straight as an arrow at any speed is why I say it's not your prop. It is a very sensitive plane and only requires small inputs (34" span and throws are only 1/4" up/1/4" down for full elevator)
Having said that, I would drop down to maybe an 8x8 or 7x8 (if there is such an animal). You want the higher pitch to get the higher top end. Mine sags a bit on launch but pulls out nicely after about 40' and will hit 100 mph on the straights.