I can't speak to the performance, or the smoke, unfortunately, and here's why:
When I deleted the cats, it was after I had put my engine back together with Colt Stage 2 Cam, bigger turbos, and a Malone Tuning custom tune. I developed a problem with the engine going into limp mode, after about 3500 miles due to one of the turbos not spooling properly compared to the other. One of my thoughts to all of this was maybe the catalytic converters were clogged on one side, so I gutted the cats hoping that would solve my problem, and unfortunately, it did not. So I took the big turbos out and put the stock turbos back in, and then the problem was solved. However, I still have a custom Malone Tune, and if you drive it hard, it will smoke. But I can't tell if gutting the cats made it smoke more, due to the tuning prior to gutting them. Also I can't attest to any performance gains of gutting the catalytic converters on the stock engine and tune, due to the tuning and Colt Cams. However, I have not seen a difference in mileage. I think that mileage is more directly associated with how much right pedal is being used. That seems to make the biggest difference in mileage to me.
So basically, I have no clue if it smokes more with the cats removed, or if there was any performance gain by doing so. Sorry I can't answer those two questions for you.