I have seen the numbers, and here is a chart that details that information:
You are right, there is a huge difference between wood bats, -5 bats, and -3 bats. Its remarkable. Where you and I differ is the culprit of this. I personally believe that players are getting exposed as bad hitters by better bats, not their mechanics. I've seen players in the Houston area that are highly regarded high school and college guys swing metal one round and wood the next off of BP and get owned. Yes they made adjustments to their swing, but they could not handle the wood. A coach once said to me, I can't make a donkey into a thoroughbred but I can make a donkey into a pretty good donkey. Thats what I think bats do. Wood bats will show you who's a donkey and who's a thoroughbred. Some players can make adjustments in their approach but I would say most cannot. The woods elimate the cheap hits (off the handle, off the end, a near barrel hit) that metal bats still shoot into the gap which cheapens the game. A coach can attempt to improve a player's swing until he is blue in the face but if the player is not capable of making the adjustments then what was the purpose? The coach may not have put a number on it, but he does claim he can fix it and I just don't think that is possible and gives players or parents false hope.