Tom,
From what I've read about the style format, you will not be able to play the T3 or T4 styles on your T2. However, the T3 and T2 styles will play on the T4.
As for the midi files, they should play the same, but keep in mind they can be revoiced to include some of the new T4 voices using the onboard Song Creator program.
Cheers,
Gary
_________________________
PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)