My order of preference, PS 6.1 90>KPS 88>K90>PS 85>Ncode. I don't like how stiff the Ncode feels and the K90 is somewhere in between. The PS 6.1 90 is the easiest Pro Staff to swing and still keeps the feel of the Pro Staff line. The KPS 88 was a sledgehammer but was very difficult to generate racquet speed compared to the PS 6.1 90. If you could generate massive racquet speed, KPS 88 is the racquet for you.
I keep forgetting that these have a much tighter string bed compared to my Babolat Pure Storm Tour GT so if you are coming from another frame that has a rather open string pattern, drop the tension at least a few lbs to reduce the string bed stiffness.