Which head/combustion chamber is better for performance? Speed master aluminum LA or aftermarket magnum iron head?

pittsburghracer said
There are some pretty nice magnum heads out there but the trouble is they came on Mopar crate engines or other sources and are no longer available. A friend has a set on his 408 based engine that runs 10.70’s. (2.05 valve). Edelbrock, Speedmaster, ProMax, TrickFlow, etc can be made to go a lot faster. But all require extra work. As did the magnum heads on my friends build. But like it says above more info is needed
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Mentioned were Edelbroor Performer, TrickFlow, Speedmaster and ProMax heads. What about the 1970 and 71 stock 340 heads with the large 2.02 valves? Are any of those aftermarket heads better/worse? The literatures says "increased performance". Performance doesn't necessarily effect gas mileage. What's the story?