I BELIEVE (always dangerous) that the 5.7L Eagle heads flow about the same as the 6.1L heads, they both have the same port opening, so you can more easily put a 6.1L intake manifold on a 5.7L engine.
In terms of potential, they are also about the same. Both can be ported to flow 350+ CFM. The 6.4L Heads are even better since they come with a larger intake valve and the 6.4 L motor has a slightly bigger bore which means that the intake valve has even less shrouding by the cylinder wall.
As always keep in mind that people don't race flow benches. I once read an article about a set of 351W Ford heads. They put up some huge numbers, then I read the details, they flow benched the heads with 4.250" bore which was WAY bigger than the stock 4.00" bore. Thus, the flow bench numbers were largely a work of fiction.