ive fitted the 18x9 +26s onto my old e46 sedan. I ran a 225/40/18 and they did no protrude past the guards..they were rolled though and i was lowered..i guess if you play around with camber, you'll get it sitting nice. You can run a square set up easily. a 235/40 should be sweet since you have a coupe which has abit wider guards than a sedan.
i also fitted a 19x9.5 +27 with a 225/35/19 tyre and they was flush as fk! i loved the look.