pgt: The problem (as I see it) with your proposal is that it doesn't just measure the speed of the player, it also measures the speed of the opponents of the player. With your proposal, a slow player that plays mostly against slow players will still be able to collect "fast player points" - his opponents aren't fast so it's easier to be below the 10% margin. A player who plays against fast opponents has to work a lot harder to get below the 10% margin.

I think it's the intention of your proposal that the second player gets ranked "faster" than the first.