Why such a modest passmark score increase in single vs dual CPU?

I understand a bit about having more cores vs having faster cores and how this plays with different workloads.

A single E5-2690v3 CPU has a passmark of 18k, while the dual CPU variant only increases that to 25k. Why is the increase in Passmark score between single and dual CPU so modest.

Relatedly, if these CPUs are being used in a VM server running KVM, would pinning specific cores to VMs provide a total possible throughput equivalent to a score of 36k ?