Here are the remaining six exposures, again with no adjustments or color correction to the images. Aperture was held constant at f/11; shutter speed varied in one-stop increments.
Notice that the variation between exposures is not linear, which I wouldn't expect it to be. (Digital sensors are more responsive to higher light levels.) Alan found that Zone VII-1/2 was the highest placement that would retain highlight detail; that's confirmed here, where the Zone VIII exposure is just plain blown out. At the low end, though, there is still a bit of room between the Zone II exposure and absolute black (much more visible on the original, and in a print, than it is here). The exact gray-scale value for each exposure is given in image #4 of this series.
I also wanted to quantify what Lightroom adjustments could do to "rescue" the highest and lowest exposures. As shown in the insets, the Black slider, moved from its default value of 5 to 0, lightened the gray card to about Zone II-1/2; the Recovery slider, moved from its default of 0 all the way to the right, lowered the gray card essentially one full stop, with some useful extra detail showing in the gray scale. Again, this is with RAW files; I wouldn't expect JPEGs to be as forgiving.
My take-away from this: exposure for digital shooting really is similar to transparency film, as I've read many times. Even knowing that I've got a little bit of leeway at the top, I'll definitely keep important highlights within the range that Alan recommended.