You're going to want 18s. That is the smallest size that will clear the stock brakes without going fully custom.
I looked into a set of drag race rims at one point, and talked to weldracing at length about it. They said there was a possibility a 17 COULD be made to fit, but you would need to do all of the measurements and even then they may not be able to do it.
As I said, and the others here said, go with 18s, and then you can use the ford recommended size of 235/55/18 or similar depending on your tire length, stock 18s are 18x8. They come on the SEL model.
For reference 114.3x5 or 5x4.5 is the bolt patern. Any rim that fits the 2010+ mustang will fit the SHO just fine. I ran AMR wheels from American muscle on mine for a while.