Interesting question. Thinking about it, I would be tempted by the "R".

Best quote I saw on moire: "The patterns are generated when an image with too high a spatial frequency is captured by a sensor. To avoid moire, the sampling frequency of the sensor has to be double the spatial frequency that reaches it."

So it stands to reason that the higher resolution your sensor, the less likely you are to have moiré. So if patterns in nature are only causing moiré infrequently with ~20mb sensors, wouldn't they even be less frequent with the 50mb sensor?