1. A method for optimizing a drilling operating parameter for a drilling system, the method comprising: (a) entering a plurality of drilling system design parameters into a trained artificial neural network, the drilling system including first and second longitudinally spaced cutting structures on a single drill string, the design parameters including design parameters for the first cutting structure and design parameters for the second cutting structure, and processing at least one the design parameters of the first cutting structure in combination with at least one the design parameters of the second cutting structure to obtain at least one combined design parameter; and entering the at least one combined design parameter into the trained artificial neural network; (b) entering at least one property of an earth formation to be drilled by the drilling system into the trained artificial neural network; (c) entering at least one drilling operating parameter into the trained artificial network; and (d) adjusting a value of the at least one drilling operating parameter in response to an output of the trained artificial neural network so as to optimize said drilling operating parameter.