67 camaro intake manifold

I have a 67 with a 350 and cam with .454"/.488" lift. It has full roller rockers. The manifold is a standard Performer and the carb is an Edelbrock
600 cfm. I have headers and 3.08 gear and TH350. I want a Performer RPM manifold. Or a Holley 750 cfm. What would be a better upgrade for speed? Thanks
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