Theres no reason to even mess with the 6port engine unless you were going to throw a turbo on it. Sure you can rebuild it and port it but even with a standalone you will only hit around 200rwhp MAX.. If using the stock ecu then you can dream of that goal but it's very unlikely. NOW, if you want to use 4port irons you can Streetport the hell out of them, keep it non-turbo and throw a megasquirt on there and reach some good numbers ALOT easier. I say throw a 13bt in there, all you'll need is n332/n333/or n338 ecu, n318 pressure sensor, tii afm, and knockbox. Change a couple wires on your n/a harness, get a driveshaft made or just locate all the TII rear end parts <(my choice)

I have some s5 intake manifolds, I can sell you one if you like . It sure does make the engine look pretty, and gets ride of the hideous s4 one.