If you are not planning to buy OEM or very expensive aftermarket wheels, I would say it is a moot issue. I cannot imagine any cheaper AM wheels will weigh in at close to the OEM 19s or 20s.

And more than acceleration, I would worry about the detrimental affects to slowing and turning in.

I have heavy wheels on one of my sports cars and the handling is terrible with them. Bad enought to definitely be felt.

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2006 X5 Sport 4.4i