If the car passes the emissions test without the cat fitted that is ok. It is only a fail if it fails the emmissions test. Emmissions tests after 1994 (I think) are based on cars with cats fitted as standard and are therefore much lower, so pretty near impossible to pass without the cat fitted.
The 16v cat doesnt look to be very restrictive, I have a de-cat fitted to my 16v and it does appear to make a differance to the pick up, and seems to rev a bit freer throughout the range.
Ess Three who posts on here did a comparison on the rolling road with his and didn't find a great deal of differance. He also did dyno tests on standard and after market exhausts like miltek with combinations of cat, de-cat, and race cell cat and he didn't find a great deal of differance in any of it, I seem to remember 2-3 hp max.
If you want to fit a decat the cheapest I found was the raceland one from Hottuning on ebay (put in a low offer), this comes with the lambda sensor hole. Or get a cheap secondhand cat and rod the core out of it. Having a second lambda sensor makes the swap easier at mot time if you can leave it in the cat / decat and just unplug it at the wiring end.
Paul
