Combing over EJ, running tests with my DK friend and talking to other DKs I've drawn the conclusion that almost every single Frost/Unholy combo build is putting out sameish DPS at the moment. Weapon type irrelevant. I guess it's the balance Blizzard wanted.
If I played a DK myself, I'd be sticking with 32/39 but moving to slow/fast. 32/39 is a very... I guess "comfortable" build. Tons of AoE utility, tons of pet utility, it's just a nice build with the revamped NotD and Corpse Explosion.
As a healer who doesn't suck ass, I watch pets, I heal pets, and let me tell you that fucking perma ghoul is USELESS without NotD, however with NotD it VERY rarely died and when it did, it came right back out due to the CD reduction with Plague Strike usage.
That Ghoul puts out 400-500 DPS in a decent 10 man. Simply having that thing not die on impact is going to smooth out a giant chunk of the DPS nerf in a lot of cases. NotD also works on Gargoyle and I believe Army of the Dead as well.
Army of the Dead can put out 1200-1400 DPS during it's duration, so if you're smart with it as well, it can be a great boon, and no, before someone says it, it does not taunt raid bosses.
Also: I disagree with KT 25 being more difficult. There's more to it, yes, but if anything it's even easier with the utter DPS rape you can bring with heroic buffs and healer variety. The MC is not a big deal and if anyone ever dies to Frost Blast in your heroic raid, your healers are failures. I solo healed this as a Paladin in 10 man last night after our sissy Priest "needed sleep" and no one died despite having four melee. Glyph of Holy Light FTW.
The only 25 man fight I'd say is legitimately more difficult atm is Patchwerk. Everything else is par or easier, usually the latter. This needs to change or loot needs to be par between the two.
But the moral of the story remains the same: WotLK's Kel'thuzad encounter is a joke. OS+2/3 Drake's aside, Malygos and Sapphrion, while not very difficult, can at least give you a run for your money if you botch things and press you a bit.