Using a larger diameter pipe will be fine, just make sure you use a proper coupler where the 2.25" meets the 2.5" pipe.
A larger pipe tends to give you increased flow with slightly better HP at high RPM but sometimes a little less mid-range torque due to the loss of back pressure.
I think the Magnaflow full cat-back system uses 2.5" pipe.
Straight lines are for fast cars...turns are for fast drivers
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'06 650i Cab - daily driver
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