You want to move from using physical servers to using virtual servers/machines (VMs) while utilizing the same hardware that is currently in place. You need to make sure this is possible, what feature must your CPU support?
If your processor does not support virtualization you cannot run VMs on the server. Hyperthreading and multicore processors are nice-to-have but not essential. Dual voltage options are for power supplies, not processing.
In computing, hardware-assisted virtualization is a platform virtualization approach that enables efficient full virtualization using help from hardware capabilities, primarily from the host processors. A full virtualization is used to emulate a complete hardware environment, or virtual machine, in which an unmodified guest operating system (using the same instruction set as the host machine) effectively executes in complete isolation. Hardware-assisted virtualization was added to x86 processors (Intel VT-x or AMD-V) in 2005 and 2006 (respectively).
Hardware-assisted virtualization is also known as accelerated virtualization; Xen calls it hardware virtual machine (HVM), and Virtual Iron calls it native virtualization.