The SS lines are suppose to firm up the pedal response because it doesn't expand like the rubber brake lines when under pressure. The premium brake fluids boil at a higher temperature so you are less likely to get bubbles in the fluid if you overheat your brakes.

Do you need these benefits? If you don't track/autocross your X5 then I would say no. You might feel a difference with the SS lines and some of the premium brake fluids might absorb less water. Only you can decide whether the $100-$125 it might cost is worth it.

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