I run a square setup on the track as well--275/35-18 Nitto NT01s on 18x10" Forgeline GA3R wheels. Before I tried this I was also worried about tramlining or heavy steering with the 275s up front, but it hasn't been an issue on the track at all. As said above, the improved front-end bite is fantastic. Obviously the Nittos are R-comps, but the turn-in and braking on the track feels so much better with this 275 square setup compared to the stock 245/265 PZeros or my regular street 255/275 Pilot Super Sports. Dinan Stage III suspension with -2.5deg front camber, -2.0deg rear camber. No rubbing.
The rears are a bit more tucked in than the fronts with the square setup, but the aesthetics don't bother me on the track. You could always play with using a spacer on the rear on the street to push the rears out a bit more.
Here's a picture in the driveway and on the track:
IB E90 M3 ZCP returned to BMW FS