I 5 box on a Quad core Mac Pro, 8 gigs Ram, and a GTX 285. Have an SSD and run all copies from the one directory. Plexor used for the broadcasting.

I use one 30" monitor but run the games windowed at 1920x1200 max effects for all 5 copies. I use Spaces to run all 5 copies in the same place/same res on each Space. Simply hotkey Ctrl+1,2,3,4,5 to each Space, and I have near instantaneous switching to any client, even at that resolution. You can even use Expose to see all 5 copies running at once if you want. Impressive stuff given it's all at the OS level.

Compared to the years of dual boxing on a high end PC this setup is much more stable & more usable. OSX just seems more capable at multi-tasking multiple high end applications.

Use a N52 speedpad for handling all the extra bindings needed. Just got a G13 and quite impressed so may switch to that.

Dalaran is still laggy, but that's the only place I'm not seeing 30fps constant. I just avoid running all 5 thru there on follow