If its a open induction kit bin it, it will loose you power. IIRC the only alledged proven exhaust for gains wise is the Supersprint race one.
Ktec stealth is a good bit of kit and the Yozza sport is a very good quality build (based on the supersprint) although very loud and expensive to buy.
Conversions, cams, nice gains but cash vs gains you can do a lot better. TB's will get you about 200bhp but the conversion to which whips STI Scoobys (see youtube) etc is the 250bhp 4k supercharger conversion from RS Tuning in Leeds.
Iv been in it when it was running 270 and its seriously insane. Uprate the bottom end and match the boost and you could be talking mid to high 300's maybe even 400's