Try on severl different brands & models of helmets. They fit different head shapes. I have a Scorpion EXO 400 full face. I have no problems using my peripherial vision, the venting is good and really helps keeping the bugs out of my teeth, not to mention I wear glasses and they stay securely on...
I've got a Honda SH150 and have loaded it down with a case of water, 12 pack of Diet Cokes, 2 bags of groceries, and filled my backpack as well. Hallelujah for bungee cords and cargo nets.