I'm sure it is impossible to produce a visor that can withstand anything. I did hear at the time of my accident that an F16 pilot actually lost his head hitting a bird. He had his visor down. 2 kgs of Mallard at 500 mph is a lot of energy.
As for today, I have no idea what protects our gallant pilots. For me, I have a carbon fibre propellor and never exceed 180 kts!