I 5-box, though I have 10 accounts total (with 6 active at the moment). I had leveled a character solo to 60 and then purchased a second account to level alts via instance runs, and once I found out about keyclone and this site, it wasn't long before I was running five accounts. I had considered getting 10 to run 10-man raids eventually, but have shelved that idea for the time being.