I want to say I have heard that the cast iron R/T's were better than the old EQ's which were better than OEM. So that is how I would rank them.
For a stroker build, I would guess even an R/T head would limit them without some work unless the cam was pretty mild.
For a stock stoke build, I would say the EQ's or R/T's would be fine depending on the cam.
For a stock Magnum build, I think even the current EQ's are fine as the cam is the bottleneck.
But I am not someone that would give advice on these things so they are just my guesses.
No real idea on that. If the Speedmaster is a ripoff of the Edelbrock aluminum head, I would guess the Speedmaster would have better ports. But complete speculation on my part.