True that John generally down-rates his TMX (for example to 64-80 for normal development) like many of us end up doing, but each person should do their own test and figure out what works for them. It also depends on the developer and procedures.
The nice thing about all these current films - including Tri-X - is they have long scales. So under a wide variety of conditions, giving a little more exposure to ensure you get full separations in the shadows, doesn't cost you anything in the highlights. But if you find, like Mark, that box speed gives you everything you need, it makes perfect sense to expose at box speed.
At the end of the day the biggest differences between Tri-X and TMY-2 are in image structure (granularity, resolution etc). TMY-2 is an exceedingly fine grained film for its speed. It is actually more comparable to say Delta 100 in graininess than any other 400 speed film. Another favourable characteristic of TMY-2 is reciprocity behaviour, if that is deemed important to a particular individual.