As I said, when you get stuck in, it is a great power. Just doing wounds to multiple unit. *Someone* will fail, and that's a couple wounds there.
It is really silly to think of it as 'only 40%'. Look at Tyranid Guns... most of them don't penestrate armor, so a couple wounds on marines is usually saved. If you hit targets like Centurios, or Terminators, Psychic Scream is painful.