Well, this is a difficult question, but you said it in your post Michael. Edge effects vary so much with emulsion and developer that it is impossible to say anything definitive about anything here! I can have a 3% Iodide emulsion in D76 and the edge effects will vary based on the placement of the Iodide during precipitation. So, emulsion is a factor. Then comare D76 with (a reach but an example) Dektol with one emulsion and you see something else.
I can design 5 or 6 developers to maximize any factor, but which is best. This is what the old timers found. There is no magic bullet.
I'm trying to design an HA developer right now myself. Wish me good luck!