I think your DP will help a lot with producing much more linear curves. What rev. or V5 do you have? I'd be interested to see how the single exhaust sounds / performs with the downpipe without a split. I've been one that always wanted to do that! I was even thinking of test fitting the F30 exhaust to see if that puppy will work since its a single turbo back with a cat.
Intercooler I think is a must with this car, as Kalud said... stock cars run hot and the computer robs power. My intercooler helped out a lot in that department, but dont forget about the airflow variable that you area also changing for the better. The stock ic seems to have a lot of turbulent piping as well as the poor design of the unit as a whole.