Do you have links to XFI and fast system? Will they work with the transmission? Also, what about the "drive by wire"? The thing I like most about the Mopar harness is that it is idiot proof.
X2! I don't know anything about the XFI and fast systems. But I would like to see them and the $$ they cost.
There are cheaper ways to go the wiring (way cheaper!!:-D). Street and Performance, Auto Hotwire, etc, etc, can do harnesses for around 1000 or less. These will let you use all the stock stuff... DBW pedal, computer, etc. I have talked to the Auto Hotwire guys at car show. Nice guys and their harness is like $750 plus whatever to flash the computer(to get rid of security codes and stuff).