Update on this. A crew member bought a Princeton Tec Apex and (4) 2300mAh LSD Energizer AA's (I tested my own 2300 Energizers to actually have 2300mAh). He says that even on "low" he's only getting 1/2 day out of the batteries. He says the light output is a good balance of flood-throw. He's really just disappointed with the lack of runtime. Now the other issue is that he's lost the wall wart for his battery charger (it's a Tenergy 10 bank or 8 bank "smart" charger) so he's been unable to recharge the batteries to try them again. He's been using Alkalines since (which apparently give the same 1/2 day runtime).
Something seems fishy to me, as this headlamp on "Maxbright low" is spec'd to run 8 hours.
I wonder if he should have just gone ahead with the Fenix. Maybe even the LED Lenser headlamp H14R which I own a clone of.
I don't have the HP11, but I have the HP10. Assuming they're very similar, I think the HP11 would be a great light. The main reason I don't use it much more is because it weighs so much. I've slept several nights with it on my head, so I think the wiring is durable enough. The diffuser is a great option too. If the head is the same size as the HP10, I can tell you that the diffuser for the Xeno e03 works too. It looks silly, but it makes the headlamp into a great lantern for everyone. The battery life is what I love most about this light.