Meeting with a M4:
We've made a small comparison on the Autobahn. Good results for my small Z4 -> from 80 to 260 km/h no winner.
Latest update:
JL Carbon fibre trunk spoiler lip installed onto a 2nd (new) trunk.
Due to the very very very very poor standard fitment of the JL Spoiler, I've bought a new trunk, because a lot of adjustment must be done to fit the spoiler. My "naked" OEM trunk will be re-installed when I'll sell the car anytime.
Next mods:
Lightweight front splitter (with TÜV technical approval = street legal for Germany)