Does this look like detonation?

[JMD]

Hi all, the engine in question is a 454 with a mild cam, aluminum heads, and a 9:1 compression ratio on 91 octane gas. It’s controlled by Holley’s sniper EFI.
So I’ve been messing around with my new Holley Hyperspark electronic ignition and it’s definitely made the truck more responsive. I’ve been slowly bumping up the WOT timing, but I’m worried I might have gone too far advance. I currently have the controller set at 40* advanced. I know, that’s way too much. However, I’m pretty sure the cheap timing pointer and harmonic balancer combo I have does not give an accurate TDC reading whatsoever. This means that my 40* of advance could be way less.
I haven’t heard any detonation, but that doesn’t mean it’s not there. I pulled a few spark plugs and for the most part they looked great (a nice brown color) except for #6 which is pictured below. Is this what detonation looks like or do I have a different problem?