[GothM]

With my 245/40 275/35 set up on Nitto Invos I was surprised the sidewall actually ended up being taller than the stock 45/40 set up. I ran into a similar issue on my M3 between Advan Neovas and Hoosier A6s both identical size but the Hoosiers being taller. That is typical from my experience with race rubber though. So between brands you may find that the side-walls vary slightly.

Depending on the tire you might get a little pooch effect but unless it is substantial, you are really one with your car or driving competitively and keeping a data log you probably wont notice if the diameter is slightly off.

If your time/budget allows it is fun hit the track or auto-x to experiment with tires to see how they effect your car.