I have stainless steel sports cats on what is allegedly a Tubi exhaust on my 996T although for all I know it could be any other quality after market system. I don't know if they are 200 cell cats but the noise from the rest of the system is redolent of air-cooled 911s and is not too loud; at least I have to say that when followed by a police van for several miles in a traffic queue with continual stops and starts the police were not disposed to pull me over for a loud exhaust. It is generally understood that power increase claims for air filters and exhausts are "best possible case in ideal conditions" scenarios, so without changes to the inlet, on a turbo at least, you could end up blowing out what you have just blown in with a straight through pipe because of the lack of back pressure, and to a degree, any engine that is designed to work well with an exhaust system, might not, as a stand alone mod, benefit much from simply bypassing the cats. I believe it is generally understood the the std 996 exhaust is a bit restrictive, so there is some improvement to be had.
These days it is so easy to back track, electronically, the date, time and location of the mot test, I would not recommend accepting the assistance of a "generous" tester, because you will be amazed at how quickly his or her "support" will disappear if it all goes pear shaped. Just my two penn'orth.
