...I rarely use their voices (perhaps my taste in music is weird!!!!) as they just seem to use the same formula...
I know what you mean and I agree -not about you having weird music taste, though.. maybe "unique music taste"

It's impossible to decide about keyboard in shop, if staff is too much concentrated on selling (instead listening to customer).
As I said in previous post, don't buy if you see no benefits for you. Yes, SX900 is better than S975, but only if owner uses (or need) those benefits. In general, differences aren't huge, though. As we use to say, it's the musician who makes the difference, not the instrument.
On the other hand, some new features, can be very tempting... and at some point we just empty our wallet

Bogdan