This paper addresses several key issues in performance evaluation for the comparison of existing multichannel space-time processing (STP) approaches, with application to airborne wide-area surveillance (WAS) radars. Included are the selection of appropriate performance measures, the definition of degrees of freedom (DOF), and a performance comparison of the factored approach (FA), the extended factored approach (EFA), and the joint domain localized (JDL) processing approach. As the clutter environment is severely nonhomogeneous, our study shows that a probability based measure for STP evaluation and comparison is more objective than an output signal-to-clutter-plus-noise (SCNR) based measure. We also propose a separation of the system's available DOF and the processor's DOF. The STP comparison shows that the JDL approach outperforms the FA and the EFA, especially in more nonhomogeneous clutter. A discussion of several ongoing and future efforts is also presented.