Using RAF and 5 boxing this can be done in 5-6 days /played without boosting. I did this without rushing and having fun doing instances along the way.
You can have 9 lvl 60s on 1 account by lvling 3 teams to 60 but that is not optimal. This is THE lowest amount of xp aquired where this is possible.

The important thing to remember when doing this is that you get your first free grantable level at lvl 3. So technically you only get 29 lvls when you reach lvl 60.
The reason to lvl a team to 60 and not just 59 when you get your last grantable lvl is so you can grant everyone up to 60.

I made teams of all similar classes to speed up lvling by only having to do 1 class's quests. I also put what I felt would be the easier teams to lvl 5 boxing in the slots that require higher lvling. Feel free to substitute to your liking.

Step one: Solo level a pally to lvl 3 then a warrior to lvl 3 then a rogue to lvl 3. (15 minutes total)

Step two: Level a team of priests to lvl 7. (45 minutes)
Grant pally, warrior, and rogue up to lvl 7 each.

Step three: Level a team of hunters to lvl 14. (2 hrs)
Grant previous four classes to lvl 13.

Step four: Level a team of warlocks to lvl 23. (6 hrs)
Grant previous five classes to lvl 22.

Step five: Level a team of druids to lvl 33. (16 hrs)
Grant five of the previous six classes to lvl 33 and one to lvl 32
(six lvl 33s, one lvl 32)

Step six: Level a team of mages to lvl 46. (36 hrs)
Grant the six lvl 33s to lvl 46.
Grant the lvl 32 to lvl 42.
(seven lvl 46s, one lvl 42)

Step seven: Level a team of shamen to lvl 60. (60 hrs)
Grant previous eight classes to lvl 60!
(nine lvl 60s with 0 lvls to grant)

Total time: 121 hrs. (5 days, 1 hr)

If you include the other accounts you will have 13 lvl 60s. These are the approximate times it took me...it will save you about 2.5 days /played over taking 3 teams to lvl 60. If you know the quests and focus I bet this can be done in under 4 days.