Comment by zamadatix

4x 8 GB is still a lot easier to drive at high speed than 4x 48 GB, but yes, one factor in the above comparison is indeed the number of DIMMs per channel. Ranks per DIMM is definitely a factor as well, though on large capacity DIMMs that tends to be a one sided story. Another factor in the rabbit hole is banks, tying it all back.

The other part of 2 DIMM boards is the trace lengths can be that much shorter (they need to be the same length so fewer slots means less max length to match to).