I would say that 48mm offset would be the limit. You should have no rubbing issues with that offset. 48mm would push the wheel further outwards from the center of the car. So it would have more of a "dish look."

 

The difference in offset, in this case, would push the tire 5mm out from the car. The two things to consider: will your fender allow it and will the wheel clear the brake? If the wheel clears the brake okay, you could counteract the offset concern by using a 215/45-17 Michelin Pilot Alpin - which is about 8mm narrower total (4mm on each side) than the 225/45-17.

 

Also, Subaru's don't like low offsets. Anything lower than +44 will cause some weirdness. Steering response/feedback and input will be all wacky. Also, low offset rims will put more stress on the already weak wheel bearings causing them to wear and fail much faster.

I recommend staying above +47 for 7-7.5" wide rims and no less than +44 for 8-8.5" wide rims.

- Alex