Gear ratio is easy to figure out. You take the number of teeth on the spur and divide by the number of teeth on the pinion.

6.6:1 is probably the 66-tooth spur with a 10-tooth pinion: 66/10 = 6.6
5.33:1 is probably the 64-tooth spur with a 12-tooth pinion: 64/12 = 5.33
4.43:1 is probably the 62-tooth spur with a 14-tooth pinion: 62/14 = 4.43

As presented, you can basically use any size prop you want... You didn't say which battery you were going to use. With no battery the prop isn't going to spin, so it doesn't really matter what size you use; you'll never overload the motor

Seriously, the battery is the most important piece here. If you've got a pack in mind already, that is going to tell us what size props are appropriate.

I know the 12x6 is a good 3D setup with a 3S LiPoly and 6.6:1 gear ratio, but I'm guessing you want something more warbird-like as far as speed.