Unless I am badly misinformed there will be very little difference.  I don't think they changed the separator or walkers much if anything between the two machines.  The hsp. would've been bumped but that would be it and normally hsp. wasn't an issue on a 9600.  If you go STS I would say you will gain some capacity but my experience has been primarily in corn going from a 9600 to 9660 STS.  Once Deere came out with the STS machine the walker machine had few updates other then more electronics from what I recall.