I third exeter_acres suggestion to get a lower pitch prop. Only get a 12x4 or 12x5. Note that the larger prop will turn slower and offer a little better engine life. It will also offer good accelration and lower speed.

But frankly, a 11x6 should be quite OK. I flew my own 65" 40 size Explorer-40 with a 55AX on 12x6 for a long time and 11x7 when I progressed to aerobatics. I didnt transition to a lower pitch prop till I started hovering on my 3rd airplane.

Ameyam