When I went from 3 chars to 5 chars, my laptop could no longer keep up with rendering all the clients on 2 screens. Going back to one screen increased main window fps from 10-15 to 30-40 which made it playable, ofc this is on a huge 50 inch tv so I can tolerate having multiple small follower clients on the same screen.

Keep in mind that my laptop is a dual core 2 duo with 4 gig ram, it should be doable to 5 box for pve on most systems.
pvp is another matter however, have to wait for two more paychecks before I'll buy a new rig :S