1. A method of predicting operating characteristics of a circuit structure, comprising: obtaining characteristics of a circuit structure; obtaining a general model of the circuit structure; determining, with a programmed computer, parameters of the general model of the circuit structure such that the general model matches one or more of the obtained circuit characteristics at one or more points, and a slope of the general model at the one or more points corresponds to one or more of the obtained circuit characteristics, and quantifies a load sensitivity of the circuit structure, wherein the slope is a slope of a curve of values of one of a delay and output slew of the circuit structure versus a load of the circuit structure; employing the determined parameters to generate an osculating model of the circuit structure; and using the osculating model to predict the operating characteristics of the circuit structure.