Had my 197 at RGS motorsport and it made 179.4bhp. Its nearly done 70,000miles and has a the usual ITG filter and the silencer removed. Seems abit down to me.
In most cases it's only the secondary Cat which is removed and in most cases the car will still pass without this being present. The main Cat is in the collector on the Manifold, it seems that this does the majority of the cleaning up and the secondary one under the car is just there as reinforcement.