I think I'm pretty much finished here. I'm sure I could always go back and tweak a detail here or there, but sooner or later you always reach that point where you throw up your hands and say, "looks good to me." Well, here I am.
Here's where I'm at after a couple of hours painting. You can see here some of the decisions I made along the way to raise the cheekbones and drastically lower the top of the cranium. I think the result is a much stronger likeness overall. I'll continue to tweak the painting as I go along, tightening up the details as I go along.