It really comes down to personal preferences.
Stillwell filled my tyres to 35psi all around. So I enjoyed the drive at those pressures for the first tankful. When I filled the car with petrol last, I increased the pressure to 37psi all around. I can't really tell if there is a difference yet. Both pressures seem to be very acceptable.
I will go for 38psi next time and then maybe cycle down to 35psi to test a big change.
I was filling the E90's 17" mixed tyres with around 36-38psi and all was good.
328i M-Sport, Estoril Blue, Carbon XP 35 Tint, front heated seats, black Dakota, Sports Suspension, Anthracite Headliner, HUD, Pro Nav, Sunroof, hk 600w, Bi-Xenon, 19" 403M wheels, Reversing Camera, DAB+, Xenon, BT Ext Connect. JB4 on Map 2 with Catless DP produces awesome performance in Sport.