Stage pianos can often have different keyboard actions and are worth paying attention to, that is if you are considering a stage piano. In the case of the Kurzweil SP series, they produce a SP2 with semi-weighted keyboard action and a SP2X which has a fully weighted hammer action keyboard. Bear in mind that "fully weighted", as is the case here with the SP2X, does not mean the same a progressive hammer action (see later).
While the sounds on stage pianos is often much wider than what you would find on an average digital piano, stage pianos have far fewer voices than a typical electronic synthesizer. Stage pianos usually have a smaller selection of voices as mentioned in a previous question.