BTA doesn't matter for dual-box openers; shared bank is too expensive.
Parasitic Breastplate and Sustaining Symbiont were part of the
original gear plan, but I quickly shifted away from them when I realized I could get +10 to all saves by combining a +6 resistance lootgen item with the +4 insightful saves bracers from Shadowfell.
I think I agree that black dragonhide is better than assassin leathers. At very least they're close enough that I'll choose the dragonhide anyway because it looks a million times cooler. It's also trivially easy to farm up black dragonscale on a dual-box account, since by definition you get two chest pulls per run (~5 scales) and you can bring an epic alt from your main account to faceroll it quickly on heroic elite.