Great minds think alike
I'm going for something similar right now. It's a slow going, but it most certainly provides good results. However, problem is I don't have the Black Helmet available (but I have other useful items, like belt of luck, dagger of judgment, twinkling boots, etc.), so I guess I'll either still do Black Knights or go for Bone Dragons - or even both. We'll see.
As for the question, I think the horn will do nicely. +5 to droid's attack is pretty nice if you're bent on using the droids. The trouble is that it is an artifact and the warrior gets only 1 artifact slot unless she gets Agvares or Elenhel as companions, but still, it is a decent addition if you go the droid way. I'm considering taking Trigger with me (something I have never done) - he boosts the crit of all rangers, which includes the droids and has a gloves/belt slot, so I won't be missing out on the second necropolis gloves pair.
So many options and so many choices

Certainly makes for a fun game.