Cp and Rp effectively limit the maximum data rate which can be transferred over SDA and SCL. A high Cp can be compensated with a low Rp and vice versa.
The following three pictures show the same part of an I2C transfer. Compared to the first one, the second picture shows the signals with a modified Rp of 2 kΩ, the third one with a lower Cp of 150 pF.
Note: Long wires increase Cp dramatically. I2C connections should always be as short as possible and connected by a suitable wiring pattern (c.f. I2C specification, section 17.3).