Well I finally hit 70 on my 5 box team last night.

This is the path I followed.

1- 20 Starting zone.

20 - 47 Instances grinding.
DM
SFK
BFD
RFK
SM
ZF
Mara

47 - 60
Instance questing and general questing.
ST and all quests in BRD apart from EMP because I wiped on that damn endurance room, forget to clean my totems up and pulled mobs onto me when I needed a quick drink.

60 Outlands
Instance Quests of HFC BF, SP and UB.

64-> Quest grinding avoiding as many collections quests as I could, I did them if it was good drop rate and opened some nice easy kill quests.

I found 68 - 70 easy as I just focused on the group quests which are always multiboxer friendly.

Now to gear up and hit the PvE until I get bored of it and then onto PvP if I have time before the expansion