My personal favourite setup is:
RDM/WHM
RDM/WHM or WHM/BLM(BLM submainly for sleepga, and bene on the higher boss floors)
DD/NIN x4
Preferably mixing dmg types.
My Current set is:
RDM or WHM
RDM or WHM
MNK
WAR
DRK (Apoca)
Pickup DD/NIN.
Climbed from 20-100 with ease :3 Not 1 wipe. Aslong as you have 1 person knowing what to do, and can explain it to everyone (like having someone being coordinated for sequence lamps is a godsend for time.)
Alot of people use fillmode too for it (open your console on windower and type "fillmode 1" and it'll remove all walls making it wire frame. Trippy at first, but it's another godsend ;3 (type "fillmode 0" to turn back to normal). I don't personally use it, someone else in my group does and calls out mobs on vent~
It's also a good idea for your mages to grab a Cleric's Drink~ It completely removes all status downs (minus Weakness). Handy if you get an "All" floor with Cassie.
Also, make sure everyone brings sneak and invisible items. Saves so much time.