exhaust is not that important next to upgrading your fuel and internals. you can run about 6 psi on stock internals or so i've heard, but unless you upgrade your fuel by adding a 5th fuel injector or FMU, you will lean out at full boost. a lean running engine doesnt last long, so when your engine blows because of detonation, your exhaust piping will be the least of your worries
good luck, btw