Reading again, I am a bit surprised by what is said about the R here, such as it being faster... Doesn't agree with my (admittedly limited) experience, or what is in the POH...
For instance, cruise speed at 4000 ft, ISA: F172N 110KTAS & 7.1 GPH @ 65%, C172R 111 KTAS & 8.1 GPH @ 70%. Is the perceived 15 - 20 kts difference due to old engines, props & airframes? Of course, if you run a 172N at 2300 RPM @ 4000 ft you're at 57% power, whereas a 172R at the same RPM is at 79% power; that would be expected to make a difference...
Just curious and trying to learn...