There is a stigma attached to cats in the performance world. That you can't make good power with them on your vehicle. This may have been true 20-30 years ago, but it just is not anymore.
We recently installed a catalytic converter on our customers 500 whp car to be more emissions compliant and get the over-all noise of the exhaust a bit quieter. We also switched over to ECUtek from uprev on this car, so a full re-tune was in order. The car easily made 480 whp and 369 ft lbs of torque at a similar boost level to when it was cat-less, with a 8000 rpm rev limit. To make the boost curve a little less violent, we brought it on a bit more gentle, which resulted in the "20" whp loss. But in reality, on a colder day, it probably would still have made 500 on the dyno.
It is the smoothest curve we have gotten out of this much power, and shows that just because you want a race car, does not mean you cannot be friendly to the planet.
This is the same federally legal catalytic converters we use in all of our downpipes and second cat pipes.
We have a few other little changes to make to the car for the owner, and then hopefully we can get him to shoot us some driving footage.