ahemm, my APEXi N1 catback exhaust will arrive on 14th October and not too sure what's the best/recommended size for the decat pipe?! *either using stainless-steel or galvanised-steel material* some says 2.5 to retain some amount of backpressure (thus improves low-end), others' say 3 is best for whatever reason!! which is which now?! i'm bloody confused or should i just keep the OE cat-converter?! the downpipe is OE but will later drill a hole near the top flange to accomodate the EGT probe, is this location ok?!