Just a performance report:

I've got my 27 inch Imac, with a 20 inch secondary monitor. 1st wow instance is fullscreen on the 27, with the 4 slaves all taking 1/4 of the 20 inch monitor.

My instances are symlinked but not the cache folder. Will try that tonight.

I run fine just about everywhere. VERY minor lag in oggrimar/undercity.

Dalaran however gets pretty bad. I get some MAJOR graphic lag, but was still able to work through it. Will update once I've symlinked the cache folder. Don't know if this is hard-drive, processor, graphics related. Just thought I'd post.