(sorry for the long previous post)
after doing a bit more research, I think I have come to a more reasoned conclusion…
a purely Snell helmet will protect better against extreme high impacts than the DOT standard will
BUT… the DOT standard protects well in most crashes, and generally subjects your head to less prolonged deceleration. This is were people consider DOT to be better in typical crashes.
however, a Helmet that is BOTH DOT and SNELL should protect even better than just a helmet that is only DOT or SNELL approved. After doing the research, I would buy a SNELL only helmet at all; but good thing that Most helmets that are Snell approved are also DOT.