Considering the difference in price, I would hope there would be a difference in sound, unless the T4 has so many other features ...
The tyros 5 has one feature, that makes it the only possible choice among all yamaha arrangers for me.... 76 keys.
The fact that the s950 has no sa2 voices, not the great organ section, not the awseome guitars including effects and amps, not the ensemble voices. Makes it an instrument in a whole different cattegory