Seeking the ultimate hand gun (half of the time)

[Moonwraith]

Without a shadow of a doubt, I'd go for the Hildetorrs. You can pipe them relatively easily in Forest of Sorrow, and that would be far easier than going for Delbiters. You'd also be able to do runs quicker, should you choose to go that route.

Either way, you're going to need patience. I wish you luck, you probably will need it.

the drop odds are very poor (though not the poorest) against Delbiters but they're regular monsters (perhaps even as common as dimenians in the ruins?).

Nowhere near as common, I may be wrong but I would compare them more to Chaos Bringers in Ruins in terms of how common they are.