You have to be very careful about going to other size tires than specified. The tire size specified can be the widest tire that should be used on that particular rim and a taller tire will reduce rate of acceleration. Taller tires will also lower the RPMs where the transmissions shifts. The shift points are are chosen to provide the best mix of acceleration and economy.

I wouldn't experiment with different size tires. I think, based on what it sounds like you are seeking, a softer sidewall with a tread that minimizes road noise is all you need. I don't know what your budget is but a good tire shop should be able to advise what tire is best based on how much you are comfortable spending and what you want to achieve.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas