If you're really wondering, its strong, but it will bend. The high strength boron doesn't go all of the way up to the top of the windshield frame so the frame can bend about 3/4's of the way up.
This a photo of a Boxster Spec that flipped over at about 80 mph at Willow Springs Raceway in SoCal. And this is a car with a full roll cage.
You can see that I had a window frame support bar installed with my roll cage (vertical bar) specifically to add additional support to the windshield frame.
