Well, no matter how great your gear, you still can't go faster than 12 minutes per clear; well, you can, but you just end up sitting around waiting for the instance limit to reset. I'm currently in a huge boosting binge using my druid and I highly reccomend an addon called LootAndReset. It's a little old, and has some bugs, but it does help a lot with getting an idea as to how long until you can reset and reenter without having to sit outside an instance. It also lets you reset instances with a right click which does streamline things a bit.

As for booster, I'd reccomend against a DK since the runes tend to limit how much you can do to kill mobs. Death and Decay has a long cooldown no matter how you look at it compared to Swipe and Consecrate and I found my DK to be significantly slower than my druid even in SFK. You also lose the ability to rez a slave if they happen to get aggro and die.

- Souca -