I would say that all the Tyros, each in their own time, were the Top of the Line(1 &2) and the current model is the Tyros3, therefore, have more features like sounds, styles, drum kits and in the cases, new technologies like the SuperArticulation (1st. generation)introduced in the Tyros2, and now the Super Articulation 2 in the new Tyros3.

Have established that the Tyros are the Top of the line, their smaller models counterparts:

Previous Generations
Tyros1 - PSR 3000
Tyros2 - PSR S900 Digital Audio recorder was introduced in the T2-S900

Current models
Tyros3 - PSR S910

Yamaha Added one more overdubbing Audio track in the T3 and now can also expand to more S.A.2 sounds like the new Trombone, Pan Flute, etc.

Hope it helps.

------------------
mdorantes