My school has both the older P models and the 2003 R models of the 172. They do feel slightly different in the control forces and flight characteristics. But I think that might be due to the difference in age.

I've noticed in our old 152's that every single one has a different feel. I call it the personality of the airplane. Over the years control wires have stretched, been fixed, and this has resulted in no two airplane being alike. I can almost close my eyes while flying and tell you which of the 12 152's that my school has that I'm flying.

The newer R models are completely indistinguishable from each other. They all feel exactly the same, maybe a little bit more sluggish than the other 172's. They are easier to fly smoother too.