9.4 et 34 is too conservative. 9.5 et 20 is aggressive but it will work. You will need to add some camber in the front to make it look good with 275/30's in the front. 255/35's will be stretched on 9.5" wheels but they will work and you might not need to add camber. I'm not a big fan of 265/30 because the sidewall is smaller than I would want. I would go with the 9.5 et20 wheels with 275/30 tires and have the camber adjusted front and rear. I would run 295/30 in the rear but you may have some slight rubbing. See the link I posted earlier to see what people have done to deal with the rub.
'13 SSII M3 Coupe - KW Clubsport 3-way (Eibach Front Spring Conversion), Akrapovic Evolution, ESS Tune, StopTech Trophy, IND Euro Front Bumper and Gloss Black Mirror Covers, TMS Studs/Lugs, BMW Performance Carbon Fiber Spoiler/Interior Trim/Center Console, BMW Edition Grills/Gills, BMWPedals Extended DCT Paddles, Mode Carbon GT4 Splitter, Advan TC3 (18x9.5/10.5), BBS E05 (18x10/11), G-Force Rivals (275/35/18, 295/35/18)