The CAT is the limiting factor in exhaust tuning. I'd be willing to bet that a de-CAT system would flow so much quicker, and still sound reasonable.
To lift the lid on the tin marked 'worms' again, does the fact that it's not classified as a four wheeled car allow an MoT without any emissions checking? There's certainly no emissions test on motorbikes & junking the CAT is the first thing people do when tuning.
