Does potential really matter though, if the end result shows no significant difference?
AH, I think it could
I'll take the 40's ballistic advantage over the 9mm's shot speed advantage.
But like I said, theres a limit to how small of a pistol I'm willing to run 40 through before the advantage sways greatly towards 9mm - the PM9 and 40 are good examples of that.
Conversely, I'll take the Glock 27 over the Glock 26, as I feel the 27 can be shot very well/rapidly with a little more practice - which is fun anyway.