We present a detailed performance evaluation of a hybrid optical switching architecture called Overspill Routing in Optical Networks (ORION). The ORION architecture combines wavelength and (electronic) packet switching, so as to obtain the advantages of both switching paradigms. We have developed an extensive network simulator where the basic features of the ORION architecture were modeled, including suitable loadvarying sources and edge/core node architectures. Various aspects of the ORION architecture were studied including the routing policies used (i.e. once ORION always ORION and lightpath reentry) and the various options available for the buffer architecture. The complete network study shows that ORION can absorb temporary traffic overloads, as intended, provided sufficient buffering is present.