This goes in line with the philosophy "Don't do it just because its bigger". You need to component match everything and the intake manifold is a key component in the final number. Don't think of it as "what kind of power gain can this one component give me" (which is a relevant concept), but think of it as "what can this, in combination with all my other mods, give me". For instance the greater flow capacity that this manifold provides is only relevant for NA applications and Big Turbo applications mostly because of it's increased volume. For stock and mid size turbos, that extra volume can hinder performance in the form of turbo lag by reducing the flow velocity of the charge. You will have better over all performance from the STi manifold or the JDM STi manifold for stock and mid sized turbos. Remember that the charge is under significant pressure and the same restrictions that hinder NA application becomes a non-issue. But for the 500+ HP level you are striving for, my guess would be that you will be using a large enough turbo to create the flow needed to take advantage of the volume this manifold provides.
This manifold also provide different characteristics for NA application versus Turbo applications. For NA applications the manifold is less restrictive and will provide more flow due to a less resistant path. The flow velocity becomes irrelevant because the charge is being sucked in. Technically the plenum volume can be infinite in a NA application. In a turbo application, flow velocity through the manifold is decreased versus that of an STi manifold and a pressure drop is realized because of the significant increase in plenum volume. You need to maintain a plenum size small enough to maintain pressure but large enough not to restrict the flow. Again this lends itself ideal for Large enough turbo applications. For anyone considering this for stock applications should probably re-think this as a performance mod.
