There is actually a guy on my server who 6-boxes...yes, you heard me right, 6 boxes. He has a Berserker, Guardian, Assassin, Inquisitor, Fury, and Coercer, all mid-30's...not sure how he does it, but it's probably a lot easier to coordinate HO's when you're controlling the entire group. 
I have never played EQ2, but I 4-box, on 4 computers, in EQ. I have noticed that controlling 4 toons has some adventages in that you always know exactly what the other 3 are doing at any given time. My cleric knows how many mobs are beating on me, how many are slowed, wether I am def discing etc, and can use the appropriate heal. If my first slow gets bounced I can time my second to land a fraction of a second after the mala does, instead of just before it, because I can see the casting bar on my mage. Similarly, my wizards snare or root can land right after the mala also. There is never any confusion as to which pet is off tanking what and whos job it is to heal them, because I can control them all.
Do you hate it when the wizard roots when he he should evac?
Do you hate it when the cleric wastes time and mana healing your pet when you were just about to finally get to use mend companion for once?
Do you hate it when someone gets bored and wanders up the stairs to look at the Bloated Girplan?
Doesnt happen in a boxed group.
