Exponential increases in architectural design complexity threaten to make traditional processor design optimization techniques intractable. Genetically programmed response surfaces (GPRS) address this challenge by transforming the optimization process from a lengthy series of detailed simulations into the tractable formulation and rapid evaluation of a predictive model. We validate GPRS methodology on realistic processor design spaces and compare it to recently proposed techniques for predictive microarchitectural design space exploration. Categories and Subject Descriptors C.4 [Performance of Systems]: Modeling Techniques General Terms Design, Measurement, Performance Keywords genetic programming, predictive modeling, design space exploration