Towing 4 vs Questing 5... What's faster?

Notes: On Icecrown server, Horde faction, no heirlooms.

One of the 5-man compositions I'd like to make is a DK with 4 rets. I have a level 64 DK, but I didn't know if it would be faster to have him tow the paladins via dungeons or AOE farming, or to just create 5 rets to quest, then replace one with the DK in Outland.

Has anybody done the math or compared these scenarios?

(For other towing options, I also have a ret, a hunter, and a shaman at level 80. The ret and hunter have a GS just over 3k, and the shammy is about 4k, but unless you think one of them would be head and shoulders faster than the DK at towing, I'd rather just used the DK, to get more comfortable with him as the eventual tank for dungeon runs.)

Thanks!

Option #1:

Level 1-64: Group 4 rets, have DK follow outside group, do quests and and kill tagged quest-mobs with DK. After your 4 rets are same level as your DK, include DK in the group as well.

Level 64-Max: Group 4 rets and DK, have one of your lvl80s follow outside group, do quests and kill tagged quest-mobs with your lvl80.

Option #2:

Level 4 rets until they are the same level as your DK and then level 4 rets and DK until max level. (There is no point in including a fifth Ret, if you are not going to use it for anything)

Option #1 is faster, Option #2 might give you a better feel for the team.

Edit: Questing is the fastest way to level, remember to loot quest-mobs at the same time with all your characters and have loot set to free for all. Mob tagging is allowed as long as you don't use it to kill skull-level mobs and as long as you don't do it inside instances.

Thanks for the fast reply! Although I should have clarified that the level 80 characters are all on the same account as the DK, so unfortunately, I can't have one of them follow the group if the DK is present. (I'm just getting started in multiboxing.)

I'll have the DK follow the 4 rets while they quest. My thinking of the 5 rets option was based on the added group XP for a 5th, but that probably doesn't make up for the speed of a high level toon killing once mobs are tagged.