LOL at this guy saying Jez has no idea. Take a look at his work mate. And if you think about the whole increase in boost thing. Jez is stating that for the "best results" you will require a tune/ecu upgrade. I can guarantee you that if i get a tune at 12psi and you run your turbo at 12psi that i will make 5% more power at the wheels at least.
So, his information is correct, it's just some people don't feel the need to go to the effort to get it right.