You will have the bump stop issue no matter what system you use that retains the stock edc shocks. There isn't much point IMO to getting an adjustable sleeve-over kit if you only plan to lower 10 mm. If you want the most mild drop, dinan is your answer. Dinan is however over priced. I would recommend eibach springs with e36 bump stops. I previously ran eibachs with OEM bump stops and did not notice any issues with them. Ride quality was good and height was conservative.
'13 SSII M3 Coupe - KW Clubsport 3-way, Akrapovic Evolution, ESS Tune, StopTech Trophy, IND Euro Front Bumper and Gloss Black Mirror Covers, TMS Studs/Lugs, BMW Performance Carbon Fiber Spoiler/Interior Trim/Center Console, BMW Edition Grills/Gills, BMWPedals Extended DCT Paddles, Advan TC3 18x9.5 & 18x10.5 - Hankook RS3 (Track), HRE R40 - 18x10 & 18x11 - Michelin PSS (Street)