They differ a bit in grain, but this is a very minor point. 320TXP (Tri-X 320) is a different film and offered only in medium and large format sizes. 400TX (Tri-X 400) is offered only in 35 mm and medium format sizes. They differ primarily in the shape of the contrast curve. Read about it here: http://www.kodak.com/global/en/profe...4017/f4017.pdf.
Tri-X 320 is designed for portraiture, IIRC. So far as I know, the 320 is not available in 35 mm. It has a different characteristic curve shape to make up for the difference between average outdoor lighting and studio lighting. If anything, the 320 should be less grainy.
I thought Tri-X 320 had a retouching film base, and Tri-X 400 did not. (In addition to other differences)
i still have some tri x 400 ... ( 5x7 + 4x5 )
old stuff expired in the mid/late 90s ..
it has a "tooth" to retouch ...
tri x 400 earlier than that also had a tooth ..
many films will have a "retouchable" surface,
as long as hardener isn't used with the fixer ...
i loved printing retouched tri x because
the grain also helped mask the strokes of lead ...
we used to enlarge split 5x7 negatives up to 16x20 all the time
and you couldn't see the strokes that were used to 'smooth' the uneven skin tones
you basically couldn't beat dk50+tri x and leads for portraits. great stuff ...
i am speaking of sheet films,
YMMV with tri x roll films ...
First of all I apologize for the language nasty should not have been included at all. And I am stating an opinion only partly based on Anchel's book and partly based on my experience with T max 400, classic Tri X from 30 years ago to just before the change in grain structure, and current Tri X. The difference Anchel states is in the silver crystals and grain structure with old Tri X having round crystals and high acutance, while T max has flat crystals and lower acutance; New Tri X has oval crystals lowering the acutance. Cheapening refers to the less silver used in production of Tri X and less yet in T Max. What I'm after is the "gutsy" robust, bold look of the classic tri X. HP5 is the closest that I have used.