since you can get .05 class electric motors for anywhere from $12 to $100... (more, and you are probably looking at a custom made, competition motor) and 400 class motors at essentially the same price range... Cost isn't the isue AT ALL.

The classification is simply the motor "can" (main outer sheel) size. There's dozens of different winding and magnet and bearing options within each motor class. The low end 05 and 400's won't be far off from each other in power. Going to a more expensive motor USUALLY means you are gaining efficiency, power and/or max rpm capability. (usually not all at once...)