You can put 225s all around. The difference is 0.2% - last I checked.
That's like nothing! At the top of the tire section of this forum is a tire calculator.
Having 225s all around will help make the car feel more neutral in corners. I don't think the 328i would have a hard time putting down its power on 225s.
I would recommend spacers for the rear if your go that route to make sure the car looks extra spiffy!
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