While it be on TV I have seen many elk get shot with one and they do not go very far, but as with anything you must make a good shot.  I think the thing with mechanical broadheads on elk you just do not want to hit a heavy bone(ie shoulder), but I think if you were to hit a rib you would still be fine.  I have used the Rages but not on an elk, I used the three blade on an antelope and it was totoally devastating, so I think with a good hit it should work just fine.  I would just make sure your o rings are good so it does not depoly to early.