I'm curious to hear yours (and other 5222 shooters) opinions of the difference between Tri-X and Double-X. Disclosure: I have a sneaking suspicion they are the same emulsion.
One reason is that the ISO rating of still films is a little more generous than the "Exposure Index" of Motion Picture film (you'll note the motion picture label says "EI" and doesn't use the term "ISO" anywhere). So an "EI" 250 works out to be the same sensitivity as an "ISO" 400. Of course with Kodak's streamlining lately, it would make some sense that they are the same emulsion carrying different branding for different markets.
Not trying to badmouth Kodak or accuse them of duping customers (I love and use both products, whether or not they are the same) but I've yet to come across a conclusive comparison of the two films by a still photographer using the same developer, times and exposure with both. I shoot Double-X in 16mm and have never tried it in still form but I do shoot Tri-X in stills. I feel like it has been taken for granted they are different films because they have different names and people don't realize the "box speed" is derived from two different standards.