I'm thinking of swapping my triple for double (carbon). I've got a long cage DA triple rear derailleur. If I have to replace it with a short cage I'm not going to do it at all given that I've spent a ridiculous amount swapping components, trying one way then the other way with my credit card leading the way. e.g. not too long ago I had a short cage derailleur with my triple and needed to swap it with the current derailleur. I'm not going to go out and buy another one. Gotta draw the line somewhere.
...and no I don't still have the other one.