@McHenry like @olivierlambert said, keep in mind that a VM with 16 CPUs will be less available than a VM with 4 vCPUs, because it's easier to have 4 vCPUs ready to work than 16 simultaneously
beware of this graph, it only graph the first 16 vCPU, but you can have more working !
the visual widget is failing you.
think of topology too : if you have two sockets, you can have a topology of 2 sockets with 4 cores for a 8 vCPU VM.
If you have only one socket, try to keep the topology to "1 socket xx cores" for your VMs, performance wise.