gamut size as in colorthink, the single number used to judge the amount of colors a device is capable printing. I understand that this is in direct relationship with the amount of colors and color shades I will use so the goal is comparison as long as same patch chart is used.
The Color List in ColorThink V2.3 on my computer appears to do nothing. The stupid manual is for the Mac and is written in double dutch, although it does show a single number in the list header bar. Is that the one you're using to determine gamut? In the context of the Color List, I have no idea what that number, for example, "875" colors is supposed to represent. That is to say, I don't know how the infinite quantity of different colors in any color space gets quantized in ColorThink down to a single number and how significant that number is with reference to printing.
However, as I don't print, I can be of little help in what you're trying to do. My personal feeling is that the use of a single number to compare gamuts, no matter how that number was determined, could be quite misleading.