Here's my point, pig.
With a competent instructor, the size of the plane matters not. In fact, perhaps one of the best trainers out there is the Sig Kadet Senior with it's 80 inch wingspan. Bigger planes are easier to see, and respond much more sluggishly to controls--small planes get hard to see at any distance, and orientation becomes an issue. Not to mention that a small plane with a short wing/chord will react much more quickly to control stick movements.

Bottom line--40 sized trainers are perfect for their job, so go and troll somewhere else. Anything else you say will be filed in the part of my brain reserved for idiots.