I went from three, using windowed mode, no extra programs(keyclone, autohotkey, ect.) to five, using AHK on one computer for four slaves, and main on a different computer, without much of a problem once I got it set up. I did go from three classes to two classes, which made things much easier to manage though. Gathering quests, inventory management, and other such not-in-combat things did get much more tedious though.

I did 2x hunters for a little while, got a LOT easier after getting pets. I don't really see deadzone being too big of a deal with 3x hunters before pets considering everything should be dead before it gets near you