I've been researching wheel/tire fitment for a new set by recording the details that actually worked
(or didn't) for other ZPOST members.
I find things to be more consumable in aggregate, so perhaps others will benefit from this compilation as well.
Link - BMW e86 Z4 M Coupe Wheel and Tire Fitment
Most common setup: Front 19x8.5 ET35, and Rear 19x9.5 ET25 (synthetic values based on the compiled data, not a recommendation)
Thanks to everyone on the board who shared their setup! Let me know if I recorded your config incorrectly, or if you'd like yours included.
I'll try to keep the list updated as I encounter new information (feel free to help out by PM'ing links).