Well you can't get much more aerodynamic than a full-face as far as helmets go. I think a windshield correctly fitted for your bike will be a big help. Look for one that is re-curved (an slight curve forward at the top of the shield) and it will build a nice 'pocket' around you.
Contgrats on the upgrade. The Shadow is an excellent mid-sized ride. Windshields will generate strange currents and eddies. A taller one might help. I wouldn't worry too much because you will get used to it in time. It is a new ride for you and since you have come up from a rebel you are probably running speeds you didn't do very much before.
Question have you ever watched sail boat races or motocross races? Reason I ask is if you did you could see how they will use their knees as a sail. For either catching a breeze or to contour and stabilize the gust of wind. Works well for me.
May 20, 2015 12:15 PM PDT
When I first rode my 97 shadow ace I realized almost immediately that I needed a windshield to properly enjoy the ride.The handlebars put you in a position where catching lots of wind is easy,having a shield properly mounted will eliminate that effect.
Perhaps the shield you have would work better with some adjustment.The top of my shield is about level with my eyes looking straight ahead.Make sure whatever shield you have/get is adjustable for height & tilt,sometimes just tilting the shield forwards a few degrees makes a huge difference.
Hope you have many miles of smiles,stay safe & enjoy the ride !
Plus, having your helmet properly fitted helps.