Play around with Unholy, see what you can do with it.
It won't hurt to experiment.

Most of the DK Manifesto crowd... tried Unholy because of Death's Advance.
I don't think any of them stuck with it, especially after the nerfs.

I leveled my DK's as Unholy, up until the talent changes which made Rune Tap inaccessible.
Blood actually worked for leveling, and retained the heals (was 5x DK's, without a healer in Slot 5).
Unholy has a lot of toys, but I didn't see those as easy to translate to boxing, compared to the Manifesto put forth by Mosg2.



Frost has two modes, basically.
a) Howling Blast + Frost Strike + Necrotic Strike + Blood Strike (remove this once Blood Runes are permanently Death Runes in 4.1).
b) Hungering Cold + Obliterate + Frost Strikes.

There is AoE pressure, and Anti-Healing.
Or melee range CC and massive single target DPS.
And with two hotkeys, each tied to a priority/castsequence... we can bounce between them to really pressure opposing healers.

Frost is rather strong still.
So it is an option to consider.