I've been running a square 18x9.5 ET35 MT1 (10mm front, 12mm rear spacers) with 275 NT01 rubber for a few DEs now. Camber is maxed out f1.4, r2.0. Outside edge tire wear is an issue on both the front and rear, but much worse on the front. The car is perfectly balanced, much better so that my tweaked out moton setup on my old E46. It's nearly as fast with simply rcomps and race pads. Last weekend we were running TWS clockwise; I was hitting the speed governor at the end of the straight and the brakes (HT10 front, DS2500 rear) effortlessly hauled the car back down to 80 lap after lap. Traqmate is not yet in the car, but I'm guessing, based on what a some corner-station friends were telling me, I was in the 1:57-58 range. Not bad for a car with a baby seat in the back, but still a few seconds off the pace of a well setup E46.
There is a lot of talk of a staggered setup in this thread. My recommendation is to stick with a square setup and use spacers to trim. Being able to rotate tires front to rear will give you a lot more life out of your tires. I'm going to experiment with a 10" setup and 285/295 width rubber soon. This car really needs more rubber to compensate for the additional 250lbs of weight. It also needs a lot more neg camber in the front to keep it from shredding tires. It's not a grip issue like it was on the E46 where you needed a lot of neg. camber to help dial out some understeer. The E9X has plenty of front end grip, but it costs about $50 per turn on the track in rubber
