No pump is ever designed to specifically engineer backpressure in the exhaust system for better performance. Anything you can do to decrease backpressure is good, especially on turbocharged applications. Decreasing backpressure while maintaining exhaust gas velocity is a little more tricky on naturally aspirated cars.
BMW knew that velocity and flow were very important with our pea-shooter sized turbos which is why they went with dual 60mm tubing instead of a much less costly single tube exhaust like what you would see on many other larger displacement 6cyl turbo applications.
We have an cat delete midpipe setup for the 1M that will free up the exhaust system, give you better flow, remove two cats, and give you a little more spice in the sound department. HP has been running our setup on his car for some time now.