Since I've already jacked this thread, and gabe1475 hasn't updated it in a few months, I'm going to throw in another post. Thanks to the calculator that chiefmc referenced, I found that I really should be able to do just what I wanted, which is to move the stock 175 rubber to the front, and buy a pair of 195/50R15's for the rear, all using my stock, 9-spoke Passion wheels, which are 4.5" in front and 5.5" in back. That will keep the staggered profile going that smart felt was safest for our car - I know folks are having good luck with same-sized tires all around, but I want to keep pushing-fate to a minimum.
That rubber and rim combination are within the tolerances specified by that calculator. I do not like getting blown around on the highway, but as always, I must find the least expensive solution to anything I want to do.
I guess I'm just throwing this out here in case anyone knows of any good reason why I shouldn't be able to do that, something not addressed by the handy-dandy calculator. I won't be buying new rims anytime soon, if ever, so that's not a solution for me. I'll either be painting my rims black (we see shops on TV spraying rims for big customization jobs all the time), or getting them powder coated.