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, 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, Advan TC3 18x9.5 & 18x10.5 - Hankook RS3 (Track), HRE R40 - 18x10 & 18x11 - Michelin PSS (Street)