My five DK's were/are gnomes.

I'm still considering transferring them to the horde, for Blood Elves.
But they're so far behind the pvp curve, they probably won't be fun to honor grind now.

I might go 5x DK's and then trade the Priest back to the mixed PvE heroic team.
Five DK's will be easier to manage than four plus a healer; the team would be far less competitive at higher end pvp, but still fun to mess around with in non-rated battlegrounds.