We have four Cessna 172s - and the weight carrying differs significantly depending on the model. As mentioned the S model has 180HP and the R has 160. They are identical engines with only the prop allowing the 180 to be achieved. We recently converted one of ours from 160 to 180HP. Tach, Prop and airspeed indicator were the only significant changes. The 180HP ones will indicate about 120 knots at cruise and 2500ft
For reference, here is some approximate data on ours
172S G1000 - empty 801, max 1156
172S - empty 768, max 1156
172R with 180HP - empty 764, max 1156
172R - empty 759, max 1113