I've run VRED Wintrac extreme at 225/40/18 all round on a set of 18x8J MV3 reps for 2 winters now.
If you stick to any factory (any E9x size from 16 to 19) size you'll have no speedo issues as all factory sizes are designed to have the same rolling radius. (otherwise your speedo would have to match the wheel option fitted at build)
so 225/40/18 = 255/35/18 = 225/45/17 = 255/30/19 = 225/35/19 etc etc
E90 330i 6MT gone. E91 335i 6MT gone. AMG E63 Estate gone. M6GC current...