Couple things...
Is there a differnce between helmet and hard hat, or is it just symantics?
As for the neck protection, about the only thing I could imagine is as said, the neck braces used in racing, and those things are quite limiting, and only work with a full helmet.
Also, what kind of side pertection are you looking for?? Something like from a fall or swing dirrectly to the side? I would bet you could look around and find the figures for that somewhere. Even though they only certiry for top impact, I bet they got the numbers on side as well. But on that note, I would thing taking a fall or swing to the side, if your head hit, you would USUALLY still be hitting pretty high on the helmet where most of it's stregnth is.
Sorry, just being that guy.