In modern CPUs with modern thermal management approaches, it's probable that fully loading two cores in two servers is much more efficient than even powering off the second server, because in each machine the primary delta in power draw between idle-state and max-load is in thermal management (fans), and running cores more distributed will increase passive cooling, as well as allowing the CPU cores that are in use to run in more energy-efficient modes.
That said, I haven't done the actual math here, just seen the power draw benchmarks that show idle -> single core draw -> all core draw as a curve with idle and single core usage well under the ratio of number of cores, without even accounting for the fact that each core is more performant under single-core workloads.
That said, I haven't done the actual math here, just seen the power draw benchmarks that show idle -> single core draw -> all core draw as a curve with idle and single core usage well under the ratio of number of cores, without even accounting for the fact that each core is more performant under single-core workloads.