You can do a couple of things, raise it, lower it or buy a new one.
You can lower it, the helmet buffeting occurs in a narrow band just above the windshield. If you lower if a few inches the buffeting occurs at the neck which aides ventilation in your helmet.
If you raise it to just below eye level the buffeting will be over head.
I have a memphis demon and I'm 6'. I'm confortable up until 70 or until a head wind kicks up. In which case I duck a little sport bike style.