I actually think the 6 pitch is about right for a trainer. When I've used lower pitch props on trainers, I found that they slow down too abruptly when the pilot lowers the throttle. They also have a tougher time on windy days because they don't have the speed they need to power through it. A common mistake is to try and make a trainer fly as slowly as possible. It doesn't help. I wouldn't want excessive speed mind you, but being comfortably above the stall speed of the wing and significantly faster than the wind makes the plane smoother and more predictable. Since the mind adjusts its perceptions of speed to match what it's looking at, flying at 50 mph isn't really a problem after a couple of sessions.