I'm a 3 boxer and it's a perfect number for me.

One day, I'll run up two more JUST for instancing but no way would I want to level and quest 5 at a time. I swear to Elune I wanted to stab my eyes out by the time I finished Zul'drak from all the collection quests. All I kept thinking was how sorry I felt for all the 5 boxers out there.

I have a really good RL friend that 2 boxes so we've got a pretty good thing going, atm.