I have a Boxster with a 3.4L and a Supercharger. I am running a pretty low boost setup and making about 370@the crank. Boost maxes at around 3.4psi/3.5psi at 7200 RPM right now.
With 4 PSI Boost and a better induction setup around 390 HP is achievable. The car runs great, pulls strong and sounds great!
It's a custom setup meaning that it costed more than I expected
(Dyno tuning and custom billet crankshaft pulley)