225 is the max in most tire spec catalogs for a 7" rim. Even with that setup, you are missing a lot of sidewall strength that a 7.5 or 8" would have. I have read many testimonials about how much better the same tire feels after being put on a wider rim, and it was exactly the same situation. He had E46 non-SP wheels and mounted 225's, and they felt a little squirmy. He bought some OZ 17x8's, remounted the tires, and the car felt significantly better.
Do not go any wider.