Personally i dont like the larger full size screens, they just shout grampa to me, but i can see their practicality if you live in a wet or cold climate. If you do go larger i would get one that keeps the wind off your hands as you ride too, my biggeat issue in winter is cold fingers rather than rain, even with gloves and liners my finger tips get cold at times.
Why not wait till hes up and riding then see what he thinks?