I'm running 245 f / 275 r StarSpecs on stock 18's, running at 13.5" front and ~13" rear ride heights w/ camber all the way out on the vorshlag plates without any problems. StarSpecs are wide for a street tire, but when you start talking about track rubber, you're usually talking more width than an identically "sized" street tire. You might talk to Fair at vorshlag. I know they've done ALOT of testing running wide rubber for Auto-x, but I don't know what rim widths/offsets they've been running.
///M3 '06 COUPE 6MT, SCHWARZ/GRAUR.I.P.
///M3 '06 COUPE 6MT, TITAN SILBER/SCHWARZ -- NO SUNROOF