Just remember the FIA/MSA like to change rules as often as they can! A friend bought a peltor helmet w/HANS posts and apprently its no longer legal to use in governed events!
A friend I used to work with once told me about rating on motorcycle helmets, where once there wasnt much in the way of standardised testing and making the helmets comparable, they changed the rules and found some of the higher priced helmets actually performed worse than the cheaper ones!
That said, I wouldnt ever bother getting any base line stuff, while yes they have to meet a target for safety theres a difference between meeting the target and passing it by a margin. I also wouldnt consider using a helmet without HANS posts- which of course bumps prices up and then the need to buy a HANS device, luckily the clubman is quite affordable where once it was all expensive stuff.