The Q40 planes have 400 square inches of wing, the Q500's have 500. The Q500's turn tighter and land slower.
Q40's are pretty fast. Just this weekend I was talking to a club member who did pretty damn well in F3D about 20 years ago (3rd in the WC I believe). They flew 70 second times back then. A well flown Q40 will do under 60 seconds nowadays. Close to 200 mph on the straights I reckon.
Cost is about the same. Same equipment, the Q40 airframes cost 100$ more on average.
If you aren't used to composite racing planes, get a Q500 first. These planes have very small control surface deflections. If you aren't used to that you will be surprised when it's time to land. It's like landing a glider without airbrakes: you have to be spot on, and there are no go-arounds. The Q40's come in a bit faster than a Q500.
Use JR 3421 or 3425 servos, or Futaba 9650's. Well proven servos in the high vibration environment. Use the JR Deluxe Gold switch.
Try to find a race somewhere, talk to the guys and see what the planes are like. They are no beginner planes, even when you're used to "fast planes". They fly straight as an arrow when well setup, but are very intolerant of improper setups. CG is extremely important. Take off and landing are the hard part.
Go fast and have fun!
Last edited by Rudeboy; 12-04-2014 at 03:42 PM.