Hi,
i dont know about the P1 or the Prodrive exhausts.
But Magnex, although look nice and are good quality, they are not loud at all !
I'd recommend a custom made Powerflow exhaust, my mate has just had
one fitted to his Civic and now it sounds like a beast
Its good quality too, and probably a lot cheaper than the other brands.
try these websites for more info.
http://www.powerflow.uk.com/power.html
http://www.topgear.co.uk/powerflow.html
I think I'm going to get one fitted to my XR2i
Woody.