The first thing I'd do is take half the memory out of the 64GB machine and benchmark again.

The second thing would be to swap (all) the memory between the two machines and try again.

That might tell you whether it's the amount of memory; or the actual physical memory; or the particular processor; that is the source of the difference.

Another thing worth a try would be to use whatever bios-based hardware diagnostics are available and run the memory & system board test suites.