[NAME]-Stefan R  -- I feel a bit silly to say it, but the issue was I had forgotten that the machine I was working on had an E5-2640 v1 processor in it.  The v1 of this processor only supports up to 1333 -- I had mistakenly thought the machine was equipped with a E5-2640 v2.
TLDR: I have 1600 DDR3 that I can't run faster than 1333, despite the R720 owner's manual listing 1600 as a achievable speed for the chosen configuration. I recently purchased twelve 16GB sticks of DDR3 1600 (PC3-12800R), for a grand total of 192GB.  This memory is RDIMM ECC 2Rx4 from Samsung, part number M393B2G70DB0-YK0 (all sticks are this specific part number). I was following an example memory configuration from the R720 Owner's Manual, page 46.  Regardless of the voltage, I cannot get the system to run this memory above 1333 -- a fact which seems to conflict with the configuration example in the manual which shows both 1333 and 1600. Following the example on page 46, I populated only the following DIMMS:  A1, A2, A3, A4, A5, A6, B1, B2, B3, B4, B5, B6 I'm not inclined to think the manual would be wrong, so I must be missing something.  Any ideas?
R720 memory frequency issue