diagnose this plug pic

[Nixon1]

At only 39 psi of fuel with the vacuum on, you shouldn't be running all that rich unless, like you said, you're never reaching closed loop operation, or there's some other problem, like bad O2's that you mentioned....

That's about how one of my plugs looks right now, except yours are a little worse. I think we diagnosed mine as high speed glazing and slightly lean. That was at 40 psi. My pressure is currently at 45 psi and it runs a little rich but the extra fuel gave it a VERY strong low-end boost and it's got more tip-in power now.

If you've got an AFPR, and I assume you do, I'd give it a few more psi of fuel pressure once you get the other issues sorted out. Still strange though that cyl #5 is the only plug looking like that. Do the others look similar but not as bad, or does it look like it came from an entirely different motor...?