Important to know - but we are really looking at Mobo architecture and how it affects the efficiency of the system, thus overall, dedicated OC boards will have two memory slots (1DPC). Dual density RAM can add some additional workload to the MC on the CPU - so theoretically a single density 8gb stick will hit higher speeds than a dual density 8gb stick.
The best / most efficient design is one dimm per channel, especially with single rank RAM. The old saw about 2 being better than 4 is largely related to how the architecture of the board feeds information from the RAM slots to and from the memory controllers on the cpu - mostly about the overall efficiency of different designs.
Okay - so to answer my own question (for anyone skimming):
