My CA said the 2015 X5 35i requires 87 octane (US regular). This seems odd to me because the 2014 X5 35i spec's published on BMWUSA's website call for 91 octane (US premium). Will these October 2014 N55 engine changes mean we could run 87 octane fuel in the 2015 35i without concern for pinging? If that's the case then I will order the 35i. If 91 (US premium) is also required for post October N55 engines as it is for the 2014 35i then I would order the 35d. Please advise!