In summery the advantages go long way. since you WANT to go ported NPI already as you stated in your original posts. This will provide you with the most gains overall.
Any mods you do to the engine with the ported heads will be seen very much more than you would typically. The includes , valve work , Forced induction , cams , throttle bodies , exhaust . all of that . The npi heads flow much better when setup correctly so you will not be disappointed in them at all. They are over looked more than they should be as decent castings.
In pi vs npi heads , the flow numbers are not good for any noticeable SOTP nor 1/4 power . At the shop we worked with both .
So i would say. Port them (correctly ) and you can see some nice numbers. with room to grow as you please later down the line.
GT ENGINE (temporary) 4.30 Gears , 31 spline Moser axles , Detroit tru Trac diff, Pi intake Hitech stage 2 cam, Vortech V7-JT Alum drive shaft. Lowering kit x2 ball joints Koni DA, H&R Super race spring LCA "