Also running 5 on an i7 920 (OC'd to 3.6Ghz), 12gigs RAM and gtx 480 (not OC'd) video card - runs fine with main on med settings and 4 slaves on low qual render.

I tried to split the team between two computers like Smedbox mentioned, but my internet lagged out sooo badly it was not playable and I didn't troubleshoot it much, might be my low quality 10/100 switch or something. I ended up just running all 5 on main computer and it works fine for me.