6.6/1 with a APC 12x6 SF is great for 3D. You can fly the plane really slow with confidence due to the ton of thrust it puts out. It will still fly pretty fast but sucks a lot of amps. It really keeps the down lines really slow, great for flat spins ans blenders.

To increase the overall speed of the plane, and make wind penetration better, I go with 6.0 or 6.3/1 with an APC 11x7 SF. The plane is faster overall, pulls less amps, but still has plenty of power for hovering. On windy days when down low 3D isn't the focus the 11x7 is money. If the air is still and I'm trying to really work the tork rolls and harriers, the 12x6 comes into play.

Keep in mind this is with an AON T2415-4900, it's a bigger motor than the Park or Himax. With the 12x6 - 275 watts, the 11x7 250 watts.

You can fly this plane with a 10x6 SF and pull way less amps and it will still haul the groceries plenty for pattern flying!