The simple fact is that EN 166 F is not high enough for airsoft use (it equates to 0.87 Joule impact energy). Regardless of what margins the manufacturer may or may not build in, physics is physics. Now granted the tests are for proof against penetration and under a higher impact MIGHT only crack but they might also shatter or just not stop the BB puncturing your eye. Is that a chance you're willing to take, because I'm certainly not.
The other thing to bear in mind is that in terms of industrial safety use, most companies provide EN 166 F glasses for free because they're cheap and they're legally obliged to provide some sort of PPE. If they're letting you use them for grinding, cutting or drilling then they're at risk of being open to prosecution if you get hurt because those activities require EN 166 B or better to provide correct protection (ie goggles).