I found a lot of useful information here regarding talent builds and stat weight priorities. Given that BRF encounters are mostly AoE based it seems that the suggested necrotic plague build proposed would be the best option for most circumstances once 6.1 is live. Another interesting note here is that while Multi is by far our best stat currently, Mastery becomes much more highly weighted and can even overtake Multi as the top stat priority in AoE circumstances with this 6.1 Unholy build - something to keep in mind while gearing in the present for the future. I will still likely weigh multi slightly higher than mastery in my considerations as multi is higher single target and it seems most of the critical points in BRF encounters involve single target dps priority on a specific npc.
Also, the 2pc set bonus for Unholy DKs has changed recently so most of those charts out there listing it at a ~600 dps increase for 0>4pc are inaccurate. The new set bonus increases ghoul damage by 40% when Dark Trans is up. This is a meaningful amount especially in cleave heavy fights.
I've still yet to find the simulated dps increase of the new unholy 2pc bonus but based on my calculations using sim data I'd guess it's somewhere around a 2.2-3.2k dps (@ilvl 680) increase based on current ghoul sim dps for aoe fights, and 1.6-2.0k dps increase on single target fights based on my own gear sims - meaning it'd be slightly higher for an optimized 680ilvl toon.
Given this, the BiS list for Unholy DK includes 4/5 Set pieces. But considering the minimal gain from 2>4pc I'd say it'd be better for raid loot optimization for DKs to aim for 2/5 instead, with the 2pc bonus being a large dps contributor, and the viable slots of chest, legs, and possibly helm or shoulders. Any thoughts?