Raylion speaketh much truth there.

Boosting, especially without RAF, only works if you can go really fast through the dungeons and to do that it's (imho) Druid or Paladin time. Personally I prefer Paladins, though I had a Druid friend boost me once through parts of SM and he was able to do each wing in only 2 pulls.

Dunno about DK's but Paladins and Druids will boost far faster than any other class.