Thanks all for your tips!
zXi_Gamer, I'd like to describe my task a little bit more clear.
I use virtualization to run automated soft in a 3d game in each vm, I have ~12 vms on my server. Actually I don't think allocating resources can help me, I assigned more than enough RAM to every VM and 2 cores. I disabled paging file in VMs and host, set my VMs to use RAM (added some parameters to .vmx file). My server has xeon E5 2660 ES, it has 8 cores, 16 threads x2.4mHz, also I have 64 gb 1333 ram on my server, the GPU is GTX580, ssd raid 0. Atm I have 100% load with 12 VMs, GPU load is ~35% (with heavily modified graphics settings, all lowest possible). So my bottleneck is CPU performance. Also on start I have ~40gb ram used (12x3 + server 2008 host consumption), but after 24 hours RAM usage will be almost 64gb and at some point VMs will crash unless I restart the server.
My poiny is that probably using a hypervisor (esxi or hyper-v) will provide better CPU performance (which is my bottleneck atm). Also it is interesting to learn how to use esxi 
I tried esxi 5.1, but I cannot start the game in VM (it starts, but uses software acceleration which is ultra slow, 3d acceleraton turned on in VM settings!).
After I failed with ESXI I tried to set up hyper V server. It was a pain to make windows 7 VMs work with remote FX properly, but in the end I set everything up. The funny thing is that my CPU usage decreased to ~30-35% when running 12 VMs BUT my gpu load is very high (70%+ for 12 vms) with remote FX and VMs became laggy. Don't know what to do now, but I really want to improve my server's performance, hope to get some advices.