Blood, I'm was going with a basic castsequence... well was, am experimenting with 5x Frost now.
#show
/castsequence reset=combat Heart Strike, Heart Strike, Obliterate, Obliterate
/cast Rune Strike

Heart Strike x2 (2 Blood) and then Obliterate x2 (1 Frost, 1 Unholy).
And then Rune Strike, as the Runic Power dump.

With five blood DK's, Rune Tap every 30 seconds was lots of healing.
But since you only have one Blood DK, that's what 15% health every 30s and an auto Blood Rune + Blood Tap refresh at 30% health? Something very close to that.

I would probably work Death Strike into the rotation, in the place of Obliterate.
Unless your fifth is a dedicated healer, in which case stick with Obliterate and let them heal you.

You take less damage, when Blood Runes are on cooldown, so not having Blood Runes available is a priority.




For the Frost DK's.

Frost Runes - Howling Blast
Runic Power dump - Frost Strike

Blood/Unholy - Whatever you like.
Blood Tap - Once a minute, giving you three Howling Blasts as an opener.

Mosq's DK Manifesto thread/movie has great info on Frost DK's.