Funny, isn't it - when I test rode both the 900 GT and Rally I felt quite differently in most respects:
Rideability - I thought they were much easier to ride than the 800, although the edges of the Rally's frame guards dug into the inside of my knees;
Torque - better;
Firing order - worse, I didn't particularly like the attempt to create more grunt at lower revs and emulate a twin; it wasn't necessary and created vibration;
Gearing - felt like it needed another gear (7th);
Seat - better and lower, could easily plant both feet which I couldn't do on the 800;
Centre of gravity - better, I thought the 800 had a much higher centre of gravity;
TFT - garish and a bit OTT.
I'm sure there was more but these were my stand-out impressions.