How much HP from an ECU

How much horsepower you think you will get from an ecu?
My goal when it comes in is to reach round 300-315 horsepower. Nothing huge but enough to feel it. And hopfully keep up with vettes, but that might take some more .

The more I read about the 350z, the more I think that it is gonna be like the S2000, where aftermarket intake/exhaust/headers wont help much, because the factory parts are very good already. I guess to break 300hp, you would have to get all these, plus ECU. Thats gonna be expensive, at least US$4-5,000 (Nismo parts aint cheap)