To answer your question, it will be a wasted effort to widen the exhaust port (port match) to the gasket limit. There is a gain bringing it up to the gasket limit on the roof of the exhaust port. When I port cylinder heads I'm gaining over 50 CFM on the exhaust side @ .500" and I'm not even at the gasket limit aside from the roof. Like others have stated, just make sure the exhaust manifold port is as big or bigger than the exhaust port on the head.