Tri-X 400 and Tri-X Pan 320 are totally distinct emulsions. Rather different looks, different quirks, etc. I love both and have shot a ton of both of them. Off the top of my head I do not know how to articulate the difference in look. Best way to understand the difference is to test both in your own working methods and compare results. I will likely continue to shoot both emulsions as long as they are available (hopefully as long as I am shooting!)
TXP 320 is only available in roll film and sheet film sizes.
An example shot on TXP 320 with a Mamiya 645: