Buying furious set with badges now isn't optimal. It costs way more badges than T9. My suggestion is to get 2 pieces of T9. ROV bonus is nice. And 2 pieces of furious pvp sets (especially the pvp glove) for cursader strike damage bonus. In a few more weeks, when season 8 launches, Furious will require no rating. Should be like the deadly gears now. Buy it then with honor or honor + arena points.

I don't have a lot of problems with DK tanking. Getting to tank with 2h is nice. I have some troubles on boss AOEing, (sometimes DS + bubble too late). Once geared up a bit, it should not be a problem.

Also, DK + 4 rets owns FOS and POS (except the scourgelord boss, can't down him yet), those two new ICC 5 man heroic. I cleared those 2 heroics with average gearscore of 3600 for all 5. My shamans team had like gearscore 5000 on average. And my dps drops from 4000 to 1000 when they have to move. So I sometimes still have problems on some of the bosses with shamans . On the other hand, my pallys have like 2000 dps to begin with. When I move around, they still do 1500-1800 dps. Moving, dpsing, and healing all at the same time are priceless.

With that said, there IS a bonus for switching to the setup you want: You get to utilize some of the gears more. Those gears would be otherwise sharded. Plate, Mail + healing gear, caster and tanking shield, caster ring , trinket, weapon etc. Also you get 1 more blessing for the group to -3% dmg.