A modified version of the Ampair 600 wind turbine was defined by the SEM substructuring focus group to be a benchmark for use in the pursuit of developing methods for high precision experimental substructuring. Today, seven such, intended to be identical, systems have been assembled at test laboratories within Europe and the USA. This paper reports the experimentally found dynamic behavior of five out of the seven systems. The aim of the study is to provide high fidelity data to support future component synthesis and model validation activities. Comparisons are made by evaluating deviations of measured frequency response functions and identified structural eigenfrequencies together with the correlation between eigenvector estimates. The testing is made in two parts. First, partly assembled systems, not including the rotors or the blades, are tested. This constitutes one possible and logical subsystem splitting that is likely to appear in future substructure synthesis efforts. In the second part, the fully assembled benchmark systems are tested. The test procedure, the test setup, the obtained test data and test data statistics are presented.