Mmm I've been considering PPE headers for some time. But I tell myself, if I get the headers, i'll get 2.5" piping all the way. The issue there is, I would have to go with an after market ECU as well like an Apexi Power FC. Since you're changing the size of the exhaust, It'd be best to change the ECU . So DD intake manifold, PPE headers with 2.5" piping and an ECU would be good, really good !! Now to your question about the ebay spec exhaust. First off, It mentions "Dyno Proven to Instantly Increases 10 - 20 HPS/ Low End Torque" I doubt that is true. Now one thing, it's better than a fart cannon like you see on some cars. But if you have plans to get a DD intake manifold and PPE headers, then the exhaust would be a bottle neck as the major piping is 2.25". If you were to get the DD manifold and PPE headers, then you'd e better off getting a custom straight 2.5" exhaust. If you're looking for a bit of noise and better looks, then you could conisder it. I was lucky enough to find an Austrailan ebay seller who had a Apexi Hybrid Megaphone 2.25" axle back made for the Celica. So direct bolt on. I just wanted a better looking exhaust and a bit of noise (glad it's not loud!) Though seeing that it's 2.25" and the bend is pretty much stock, here are no real performance gains. The bend in the ebay spec is better. Overall I'd say don't go for it if you want to do the mods you specified.