With most films, Diafine will give good results when rated above box speed. For example, I have used Tri-X exposed at 1250 with good results depending on lighting, and FP4+, with a box speed of 125, from my experience gives excellent results when rated at 250 in Diafine, with good highlight compensation.
Theoretically, there is no constrast control when using Diafine, as time and temperature within broad limits do not affect development, but I have read of some who have experimented with tweaking the development protocol and getting different results.
The back of the Diafine box lists 21 films and the recommended speed ratings for each, virtually all of which are above box speed. For the film you mention, it says the following:
"Tri-X Pan Pro (TXP/TXT) - Sheet; 1200"
Diafine has some other advantages; it has an extremely long shelf life, and a tremendous capacity, with soem users claiming up to 1 million rolls with the one gallon kit.