Cannot remember the source but I read somewhere that any impact over about 18 MPH and your pumpkin will not fair well. This is one of the reasons for soft barriers on tracks. I believe it is the sudden stop that is the issue. Of course a helmet is better than no helmet but...

Funny to me story, I'm riding with one of our members and I remark that his brain is far better than mine, ( DR. ) and I have a $700 helmet ... while he only has a $180 because it has a cute light on the back.... he thought about for a while and bought a Shoei 1100..