Duncan,
this is only a guess but when I fitted the Librands exhaust & manifold to my 97 +4 they told me their 200 cell would fail the MOT & was only for racing, That was a while ago, I would guess 8 years or so.
Since then I have met people who have had the 200 cell & it passes the MOT now so it must be improved.
I have no idea on the extra power delivered but a more open catalyst implies lower bhp loss due to lower pressure drop.
