The ISO speed of Tri-X is 400. The actual usable speed is about 250.
You're going the wrong direction.

 I don't have specific info about Rodinal Special but a two
stop push for most film/developer combinations requires
about double the developing time for normal contrast for
diffusion printing.
 Remember that you are not really increasing the speed of
the film, only its contrast. Since underexposure is mostly
on the "toe" of the film curve, where contrast is lower than
for the rest of the curve, increasing contrast by push
developing will help to make this area printable.
  2 stops push from the ISO speed is just about the limit
of sensitivity for most films. If the scenes have any
contrast the negatives will be hard to print because any
exposure beyond the toe of the film will be of very high
contrast. This will be true for any developer or film.
Underexposure much below about 2 stops will simply not
record on the film so no amount of development increase can
bring it out. My experience with Tri-X 400 is that around
EI-1000 is the limit if tonal rendition is to be reasonably
good.

 If you have used Rodinal Special please post _your_
experiences with it. I am not even sure its available in the
US. It is NOT the same thing as Rodinal and appears to use a
unique developing agent. I am curious about it.