Theoretically there would be no difference at 100mph. This mod is to eliminate heat soak while the car is at a stand still. There is already a s*** ton of air passing through the TMIC at speed.
Cobb makes good stuff but so does CP-E and Corksport and HKS and other vendors. Just depends on what all you want to do. I dont feel Cobb is the best at everything aftermarket for our cars so do your research. Personally I wouldnt restrict myself to one aftermarket manufaturer. If I had to right...