I have a 5 DK team that I just played out of the starting area and then parked in Hellfire Peninsula some months ago (level 58, indeed).
I played them for 2 levels (it goes quite fast now) on Hellfire Peninsula. They all are Blood spec. It is stupidly fast and easy, Death Grip, one attack, and every mob at level dies. No downtime at all, no need for heal or drink or eat. When I hit 60, I went to buy now competences, and was curious to see how they would do in instance. So I went to Remparts. I can say I never found the instance that easy with any level 60 character/group. I could not kill the dragon, although I tried several times. I will go back with fire pots. But for the rest, everything was piece of cake. I must have lost about 5 characters in total, without a single wipe before I got to the end boss. Amazing. Maybe now that I master the healing part of the spec better I would even do it easier (I was optimizing macros while running the instance. Outside world didn't give me the opportunity to need healing).
I am really motivated to get that group to 80 and try PVP with it.

As was already said, "/console AutoInteract 1" on all followers makes m�l�e boxing very easy now.

I also played a 5 beast hunters group until 60. Then I swapped one for a druid. I have a heal pet on every hunter + group heal on the druid (targeted on one of the pet), and that's mostly enough to go through most instances (not heroics, though, the pets are not resistant enough even for the simplest ones).
I am now doing PVP with that group. Certainly fun. I am not sure whether I would not prefer simply 5 hunters, though, at least for battlegrounds.

About silly options, another of my side projects is 5 Arcane Mage. I cannot wait to see them all with glyphed mirror image : 25 gnomes ! Still some way to go, they are only closing to level 67.