Porting will get you the most power.
My suggestion to you is just pull the entire motor and send it out in a big box.
Call your builder of choice (I suggest you stroll through the site sponsors and take a few numbers down)
Tell them what you want, where you ride, how you ride. They'll also follow up with a few questions.
Come to an agreement on what you want. Pay. Wait.
When it comes back install, hang on. It'll be like no other bike you've ridden if your new to this.
Next is suspension and handling.