VMware has made a significant change that when used in conjunction with the latest intel (Nehalem) or AMD (Istanbul) CPU can take a one vCPU VM performance to a new height.

 http://blogs.vmware.com/performance/2009/09/comparing-performance-of-1vcpu-nehalem-vm-with-2vcpu-harpertown-vm.html

Tags: AMD, ESX, Intel, Istanbul, Nehalem, performance, vSphere