I'm pretty sure that a 15x7" may be able to accommodate as much tire as you'd be able to run back there without the aforementioned spring relocation and/or tubbing.
IIRC, you should be able to run at least a 245/60/15 tire on a stock offset 15" wheel in the rear.
As for your photoshop, I think that looks pretty darned good!
My own personal opinion: Skip the chrome and go for the same style that you're already running...just with the bigger wheels/tires. Your car looks just about perfect as-is!
How about 15" Police Package steelies with the vented dog dish caps? Always a mean look...not sure if they make them with 5x4" bolt pattern though...
