Image capture parameters were: Gain: 18; Exposure: 19 seconds; auto white balance. Histogram upper end was 100, lower end varied between 10 and 15, depending on the image.
Stack sizes were:
M33: 2x99-image stacks combined in Nebulosity
M31: 99 images
NGC6912: 99 images
Noise stacking artifacts are visible on the M33 image; the M31 image shows very minor improvement over the smaller stack I captured last Friday (a little more dust lane detail is visible above the center of the image), suggesting about 25-35 images is the "sweet spot" for good S/N in skies with moderate skyglow.