I found this picture online of somebodys e82 but this is what I have in mind. I will be doing this soon and can post up data from track before and after. Should make it more efficient.
I had the AA race intercooler on my car previously, it comes with a shroud. The resulting Iats were not much different than my ATM intercooler with no shroud.
One problem that I have with these shrouds and stepped intercoolers is that they effectively block airflow to the lower half of the condenser and radiator, not the best idea from an overall system performance view.
In my opinion, the factory fan shroud looks pretty restrictive from an airflow exit point of view. For a track car, I would look into cutting up the OEM shroud.