I would tend to think the 5" group is the shooter and not the load, especially after shooting many rounds of a magnum. (I'm not trying to say anything about your skill. That **** is hard on your body.)
I do want to be clear about the "ladder" though. I'm not looking for nodes, flat spots...
You shot 27 rounds in 9 three shot groups, across different charges. There isn't anything statistically significant that can be drawn from such a low number of shots. You're not going to shoot a deer for groups anyway, so why does it matter if it's a half inch or inch and a half group?
You...
Do you like beating yourself up with recoil? Do you like wasting components and barrel life? I sure don't.
You're not shooting enough groups to have any statistical significance of a "node" (they don't exist), so why bother?
Purchase quality components. Use a powder with an appropriate...