This is really a post that can be answered from taking the car to exact conditions in all cases.
I have tested the B&B intercooler vs the stock vs two intercoolers I designed for my 930. On other words 4 different intercoolers. All were tested at the lab at my office with pressure drop differences, I did some testing on the street to simulate heat soak with a digital Pyrometer.
The stock intercooler is worthless even on a stock car with ZERO mods.
The B&B and the smaller IC I designed were pretty close in results. B&B performed better than my expectations.
The larger IC I designed (larger core than the Kokeln) will support around 550-600hp if not more.
Here are some pics and I have tons:
Doing some R&D work: