I would go hear the keyboard in person.

Spec-wise, the T4 has a lot new besides the choir voices.

Everyone is disappointed in the new Piano because they can't tell the difference between it and the old piano.

The difference in the drums is more subtle. I think that there are kits that have improved samples (Listen to the brush kit demo) but like most Yamaha styles, the drums sit lower in the mix. I'd love to hear comparisons of the top of the line keyboards with drums soloed.

I've heard great things about some of the new guitar and horn voices.

I wouldn't upgrade just for the new styles as many of the new ones have the choir voices.

It boils down to style and right hand voices. You don't care about the harmonizer - the other major improvement.

Demo the keyboard next to yours, for sure.

Beakybird