I can't yet comment on the Pally, but I can say the DK as a booster works well. I just finished getting a mixed team to 60 with my 64 DK (started as 63 and dinged during the process)
http://www.wowarmory.com/character-t...oran&cn=Tanakh
I know this build is not optimal, but it worked pretty well [I was conflicted when making the build between DPS and tanking talents, so it came out as a mish-mash.] It had plenty of AE damage to take down large groups quickly and held aggro beautifully using frost presence. The bottom line is I found the DK pretty easy to work with.