I had a full decat on the supra and had no issues, didn't need to swap it, but it may have been a friendly MOT centre, not sure...
The other way, although more restrictive than the test pipe, is having a sports hi-flow cat, which is what I have on the miltek system. With it already being oin the car, I couldn't tell you the difference it makes though.
With FWD I wouldn't look for anymore power to be honest, even at std on my fwd spec edit (220BHP), I was spinning the wheels too easily, which is why I traded it for the quattro, a massive difference, and much more fun!! I wasn;t going to map the fwd as it'll eat tyres.