You're right bro, 4-series can improve power, including from M Perf PPK:
The 420d M Performance Parts delivers a total of 194 horsepower and 308 pound-feet of torque — an increase of 10 horsepower and 28 pound-feet — and the 428i gets an improvement of 23 horsepower and 28 pound-feet to a total of 268 horsepower and 287 pound-feet.
The most impressive update is on the 435i, which gets an additional 34 horsepower and 37 pound-feet to 340 horsepower and 332 pound-feet of torque.
In order to obtain these updates, BMW installed a new exhaust system and remapped the ECU.