Not sure what you are looking for here. 328 does not compare in HP output with the 335, especially since the 328 is NA and the 335 is twin turbo and we are at an elevation of roughly 6500 ft. A normally aspirated engine will lose about 3% of its horsepower for every 1000 ft of elevation. At that altitude you are already down nearly 20% in power, whereas the turbo charged engine doesn't suffer from that issue. Additionally, there is nearly nothing that can be done to the 328 engine to improve it's performance, and with what it costs to make those improvements you could pretty much just buy the 335. Lowering your car and putting on a louder exhaust will make it faster on either model.
2016 Z4 in Estoril Blue.