I very much doub't a trainer would be capable of pulling 20-40 G. The wing would stall before it could produce enough lift to support 40 times its own weight. I have read on a website that said the wing for a large scale extra (I think it was Composite aircraft) was rated to 30G max and that is for a fully 3D TOC model. My friend designed a .10 pylon racer for competion. He really knows what he is doing as he wins pretty much every race he enters. When designing the wing he calculated his model would pull 20G max in a race. Remember that is for a model traveling around 120MPH and turning sharply around a course.
I think 10G is a more realistic figure for a trainer.