Mr Wilmeth is spot-on. I've got a pre-LCI E92 with the same wheel/tyre size as you. I've experimented with 10mm, 15mm and 20mm spacers and decided that 15mm front and rear is the best combo. Also retains the OEM balance of front/rear track width in that they are both 30mm wider. Oh and I'm on Ohlins coilovers...and still no rubbing issues.
E92 pre-LCI 325i - Ohlins R&T; H&R spacers; M3 strut brace; Swift thrust sheets; BMS clutch stop; BMS CDV; RE g/box mounts; Saikoumichi OCC; K&N; Cyba scoops; BMW Perf Exhaust; M3 rear spoiler; M3 white dash LEDs; LED Angels; LED side repeaters; BMW Perf black grille; CSL reps; SSDD carbon diffuser; Monster Wrap black roof