Not to start any further helmet wars but the more expensive helmets are probably very much LESS protective than the least expensive varieties.
When you carve more holes in a helmet (ostensibly for ventilation but in fact only for looks) you have to make the foam more dense in order to pass the tests. The result of this is, I believe, that LOCAL loadings can exceed the fracture force of the skull.
The testing procedure cannot tell this because it is performed on an aluminum headform which only measures the ultimate deceleration and not the local loads.
Having said all this let me also say that statistics demonstrate that a helmet that is required to perform at its limit is on the head of a dead man. There appear to be TWO distinct levels of accidents -
1) Relatively "minor" (those which do not involve motor vehicles) crashes in which the helmet us usually used well below it's crash levels because the rider lands on his hands, arms or side which mediates the head blow to levels well below those for which the helmets is specified.
2) Accidents involving motor vehicles in which the helmet is stressed at several times the capacity of the helmet.
Let's note that MOST motor vehicle accidents are not mortal accidents by a long shot. But some 80%-90% of all fatal accidents involve a motor vehicle.
There are presently approximately 600 deaths to cyclists each year so about 100 at the most are involved in fatal accidents in which a motor vehicle is not involved.
And unfortunately in my experiences every one of them is wearing a helmet. And at least two of them argued with me endlessly in internet discussions that everyone should wear a helmet at all times to "protect" themselves.
To prevent head injuries, fatal or otherwise, you must prevent "accidents" and to do this you must use your head at all times. While this isn't a 100% effective way to prevent serious injuries statistics show that experienced cyclist stand a very small chance of having a serious accident - that is one in which a visit to the hospital is warranted.