For a rubber-band mounted wing, an 11x5 on the TT 46 Pro should give plenty of speed. I wouldn't change it. That's what I run on my Aresti to keep the speed reasonable as well as gaining some extra thrust on uplines. Using an APC will add to the nose-heavy condition but will provide noticeably more thrust. To help move the GC back, try a wooden prop: Zinger Pro, Bolly, or MA are better than TF or Zingers. Does MA make an 11x5 wood prop? Don't think so...

Great plane, BTW: I flew mine yesterday with my buddy training on the buddy box.