To the OP.
I would honestly put the advice on the powertrain opinions aside, and personally test drive each vehicle (28i or 35i) with and without the dynamic handling package. Let your built in g-sensor get a feel for what its like. From there decide. In addition, if your referring to anti-roll over functionality, most modern SUVS or crossovers have that built into their stability control systems. If you were referring to ARS (active Roll stabilization found in the X5, and most F-platform vehicles) then i believe it is not applicable to X3 series (currently at least). However, the dynamic handling pack will do a great job forgetting that you dont have that option. However again, test drive the dynamic pack if possible.
BMW and Mercedes Build Beta Products!
Lexus build Release Candidate Products!
Why does this matter?
CAUSE EVERY TIME someone says Lexus has better build quality, one should consider what Toyota their Lexus Engine and chassis platform comes out of and how long that part has been tested in the real world!