Are you talking about 255/35, which is almost exactly as tall as 225/40?
Do you have pics of your setup? I have Michelic PSSs in 225/40/18 now and the setup looks somewhat stretched, it certainly looks like I could easily add a centimetre or more of contact patch on both sides of the tire.
I would have bought the PSS in 235/40/18 but that size is not available in Europe. 255/35/18 would be awesome, provided that it fits..
255/35r18 Michelin PS2's so yes. That tire is probably measured when mounted on a 9" rim. It will definitely be taller than a 225/40 mounted on a 8" rim.
You can't see to much from this picture as the tires were new, but I've noticed that as the tires wear I'm not using at least a 1/2" of the outer tread wear area. I will say this setup is for the street only. I have a dedicated set of smaller 245/40r17 hankook rs3's that in my opinion fit better and work better at the track.
At my work we just mounted a set of 255/35r18 on some 8.5's. The super sports seem to be a naturally pretty wide tire. At least in this size. They bubbled out and looked very similar to my current setup. I really feel you'll have a lot of wasted tread at least on a street car.