Peering over your spec/gear, you are over hitcap by a few points, but your expertise is low. The +str gems should be swapped with +dodge or +expertise gems if you're low there. Get an
[Inevitable Defeat] ASAP.
Ravenous Dead is a better threat talent than Virulence is. Outbreak and Dirge top Necrosis IMO, Dirge for more RP to spam rune strike with and Outbreak boosting SS damage. Rune strike and scourge strike are a lot of your boss threat and are essential components. AOE threat shouldn't generally be much of an issue with unholy. Impurity is also questionable, maybe in Naxx but once getting into Ulduar the additional magic mitigation talents become important.
Unholy isn't my preferred tanking tree (never enjoyed the playstyle as much is all) but I'd probably go with
Talent Calculator - World of Warcraft myself. IIT can be ditched for more tps talents like dark conviction, vicious strikes or impurity if another DK or warrior is bringing the same debuff to the raid. With dirge and glyph of SS you will likely not have any issues with RP generation.
If AOE threat is your concern, then you need to figure out your role in your raid. If you're an add/trash tank, then more points in AOE talents like wandering plague or the like are warranted. If you're a boss tank, then more in necrosis/BCB/single-target tps talents.
Your DPS isn't a concern so much as your TPS. If you're doing 1400-1600 DPS, that's acceptable for a tank on single targets, but it's where the damage comes from that's the concern as some talents generate more threat than others.
