I think you're looking in the wrong direction. Wing bending in a balanced turn will be no different than for a similar g force pulling out of a dive or into a climb. It sounds like what is happening is that the best turn rate is occurring at a moderate speed, which is to be expected. Go too fast and the turn rate reduces, go too slow and you stall before you can pull the required g to get a higher rate of turn. So why are they finding this is happening at a lower power setting? Shouldn't they be flying the turn at max power and using the wing loading to keep the speed back? I think what is happening is that if they genuinely flew max power max g, they'd be pulling more g's than they are comfortable with, either from the perspective of looking after an old aeroplane or from the perspective of staying conscious.
Edit: I think, reading your post again, that you're talking about actually WWII pilots, not modern pilots of WWII aircraft. In that case it'd be a matter of them staying conscious, they probably didn't care so much about looking after the aircraft beyond keeping it together enough to get home.
Last edited by AerocatS2A; 11th Dec 2012 at 04:33.