900 Watts from a 6S LiPoly is roughly 45 Amps. Sound right? Will the 3P handle 45 Amps?
The actual motor does not matter much, as long as it can handle the Volts and Amps you want to put through it. According to the specifications posted on
www.astroflight.com for this motor, it'll handle the load, but you'll be pushing its limits.
The application charts they provide list a 14x7 prop with 6S LiPoly drawing in the mid 30's for Amps, IIRC. The next thing they show is a 15x10, but only with 4S and 5S LiPoly. From that, we know your ideal prop is somwhere in between. My shoot-from-the-hip guess would be a 15x7 is the prop you want.
Is this the Funtana .40 or the .90? This setup will be okay on a .90-size, but not really 3D, and utterly ballistic on the .40-size.