On top of a dual quad core physical host, I would like to run a single VM with 8 virtual CPU (if possible) or at least 4 virtual CPU - for the purpose of scientific computing.
I have investigated what the market has to offer at this date and it seems that
Is there any solution to get 8 virtual CPUs?
Xen, KVM, VirtualBox, all can emulate more CPUs than you have, up to 32 CPUs per VM, at least.