Alright, I'm not sure if its the way IS tweaks the frame's resolution, or something else, but running IS with the instances cause a HUGE performance increase. I am able to run 4 instances, only being limited by my RAM (each instance takes ~800MB). I only have 4 GB, so I think I'm going to pick up another 2x2GB modules while I wait for my order to come in. At that point, I'll do 3 per machine. I won't need such a beefy video card for the second machine.

I do have 2 issues with IS (if anyone is still reading this thread ), which I'll do some searching on their forums for:
Background: Main session on 21" Widescreen, 2 alt sessions in the Top Left and Top Right of a 19"
1. It only happened once, but the 2 alt sessions somehow resized their resolution back to 1280x1024 pixels, but weren't shrunk into the IS session frame. So basically, the 2 alt sessions consisted of just the Top Left corner of the game screen (so that I could basically only see the char/party health bars). This is difficult to describe properly, and I'll probably just forget about it and hope it never happens again. It required a full game close and IS restart to fix.

2. When switching sessions (and having them hotswapped to the main monitor), IS never puts them back in the same order. If I switch from Main session to other sessions, then back to main, the other sessions are not in the right order.