May be some gains but the state of tune the engine is already in from the factory I would suggest they are negligible. Always worth contacting the manufacturer to see what they claim.
As said, negligible. Even if it produces a few ponies will you be able to tell the difference?
My RPI's are said to produce something like 5-7hp. Now i could say that it seems to pull a bit better at high revs but i'm sure it's all in my head. It sure sounds like it produces a lot though. In the region of 150-200hp extra!