I would guess the 3.5M has the Performance package BMW just released for the 335i and 135i. This adds extra water cooling capacity ( a secondary heat exchanger) and increases the boost slightly to produce an additional 23 wheel HP.
Less than what you can get by adding the ESS, GAIC, or the piggies ( 50 to 80+ hp), but under the BMW warranty. All of this in addition to the current 275 wheel or 306 crank standard hp.
