Why do you want more power? How do you use the Boxster - street, Ax, DE ?
I would start with Deluboz headers/exhaust system (no affiliation) - Dyno results is available.
Then, I would find wheels and tires for your intended use.
At the same time, IMO, check on brake pads for your intended use (go fast, stop fast).
Finally, if you haven't already, get yourself to the track and learn how to drive faster
If you want to talk, I am in Phoenix.
Take care,
Ed