This project was inspired by a conversation with Alan Ross and a subsequent email from him with results of a similar test that he had run. Bottom line: essentially identical results, although presented differently here.
Gray card placed on Zone V; Canon 5D MkII, 100mm f/2.8L IS macro lens; spot meter mode, manual exposure 1/50 sec. f/11 ISO 400; shaded daylight, auto color balance.
This is the original RAW image saved to PSD and exported to JPEG with no adjustments in either Lightroom or Photoshop. The slight blue cast, evident in the inset Photoshop histogram, is partially due to the gray card itself and partially due to the illumination.
The midpoint of RGB values for the gray card is exactly where it ought to be for Zone V, which is nice confirmation of the camera's meter accuracy. The small patches of black were recorded too high (seen both visually and in the histogram), but this will not be a problem for the processed image (see #3).