You could get the same tires in 12 and fit on the factory wheels..I have a friend running 28 sti outback on factory steel wheels. Most tires up to 28 inch typically come in 12in and 14in.. Even some 30's
I prefer the look of the larger wheels, and the stability increases as well. I can tell you, I think fender flare are a must even with stock tires.
Look at the rear tires, still under the rear fender.