Upgrades to newer kb's are not just about the features, functions, bell, whistles, etc...it's aso VERY much about the sound quality and realism.

As an example...I am seriously considering a T4...but the features, functions, editing, configurability, VH ect...are not even in the same ball game as a PA2/PA3. It's about the sounds.

It also depends a great deal on the type of music you play and for what purpose you use the arranger.