I spent some time going around in circles about this: I created a data-driven category using Exif::Main\41989\FocalLengthIn35mmFormat\0. The preview suggested that it would result in a non-numerical sort (e.g., 159 followed by 16). When I actually ran the data-driven category, the results were indeed sorted numerically (e.g., 159 followed by 160).
Is there a way for the preview to show more accurate results? (Obviously this isn't a critical issue, but in this case it was misleading).
The Preview is just for a quick preview and lacks all of the sophisticated sort routines available in the Category View.
In face, I'm thinking about removing the preview because modern computers are so fast that actually calculating the category is more than fast enough.