you speak like your fluent with computers, but yet dont make the simple logic of telling people all of your specs, it sounds like they are fighting for resources some where. IMO dont come in here talking about your server and all this knowledge( I dont care if you have a server or what OS you want to install on it, has nothing to do with helping you with your question), if your not even going to offer out a decent amount of information and what not about your pc. Mine runs fine 3x Vm's i7 930 @ 4.2 12 gigs ram @1800mhz 670gtx 3gigs vram <-- that is what makes this possible is it is not fighting for space in vram nor is it bottle neckeded your cpu and ram clearly are not the issue and you should know this, so listing just those doesnt give people insight to telling u anything else. All I can offer up is Mine works fine fix your settings, unless you so much want to offer up more info.
each one of these VM's have 1 cpu with 2 cores, 3 gigs of ram, they run 1 copy D3 and 2 copies of WoW each. total of 3x D3 6x WoW, I can run WoW max setting and D3 max settings main pc with out any hiccups. They are all also installed on separate SSD So that there is no interference with xfer rates or data per machine.