I based my statment about "true speed boost" on EIs obtained for HP5+ in D-76H 1:1 and 1:3 vs Microphen 1:1. The EIs were determined by the usual .10 DU above fb&f for a "Zone I" exposure using a Wallace Expo-Disc (18% transmission), and the films were developed to pretty much the same CIs.(posted 8427 days ago)My normal speed for HP5+ in D-76H 1:1 or 1:3 is EI 400, in Rodinal 1:50 it's EI 250 and in Microphen 1:1 it's EI 640. Of course film developed to significantly lower or higher CIs will have different EIs.
TXP should respond fairly similarly to HP5+, although it's been so long since I've used any sort of Tri-X I certainly can't say that for sure.
The reason I recommended Microphen specifically for this is that recently I managed to underexpose a sheet of 8x10 HP5+ about a stop and the resulting neg was a bit thin; for the second neg I used Microphen 1:1 with development time extended by about 10% and got the expected shadow density plus a little more contrast to accomodate the somewhat low-contrast scene.
Considering developer claims, though, wild speed claims have certainly been made by many manufacturers but invariably any speed increase obtained with a PQ developer as opposed to a "standard" developer is only about 1/3 to 2/3 stop especially if development time has to be reduced to obtain "normal" contrast.
Before using any new developer for important film I'd strongly suggest shooting a test film to find out for sure if the developer will do what you want and if the recommended development time is valid.