I would say that the main difference between the Rage's and the Grim Reaper's is the fact that the Rage's blades are opened before it cuts through the hide of the deer, leaving a large entrance hole. The Grim Reapers seem to be more durable, but they don't open until they are through the hide.

http://www.youtube.com/watch?v=1ZCYnbIxy8w

There's a video showing the Rage's and the Grim Reaper's going through a deer hide and then ballistic gelatin. I think they are both a solid choice for broadheads nonetheless.