the only way to really get a lower profile is to get a bigger rim. if you go wider you can lower the aspect ratio but it would stay the same overall to keep the same overall diameter. really only a bigger rim would lower the profile without screwing up the speedo.
nycstang37 is correct. You can get specs on tires easily on mfg web sites. You'll find that the slightly more than 27" diameter of the stock 17 Pirellis will be dificult to meet or exceed in any appreciable amount. If your diameter is 26" you will get an additional 1/2" space between tire and wheelwell. Stock look already has way too much space especially in the rear; that's mainly why you see so many folks (myself included) lowering the car.
I'm running 255 45 17's,they are 26" tall,they would fit on the stock rim fine but like the others said it would look funny if not lowered. Plus you would need a tuner to correct the speedo.