I don't think its a matter of potential so much as it is an issue of how much are you losing over some decent headers. Even a stock 5.9 magnum shows huge gains (like 20hp)going from even the best manifolds to a TTI header.

You have the best manifolds but even they are not nearly as good at making power as headers. The more powerful the engine the bigger difference it will make.

If your asking what is the most power you can make with those restricting the engine I would say with enough cubes, cam, compression, good heads, carb, intake... you might be able to force 550hp thgough them. Of course that same engine is probably gonna make 650+ with decent headers.