It depends on the brand and model. Sometimes the factory overclocked edition will just be factory overclocked, while other times they come with the best chips from internal benchmarking and they carry better cooling systems. The 560 ti should be better than then 560 oc though.
560 "OC" is a manufacturers designation probably meaning they added a factory overclock. With specific data on both options, it's impossible to make a comparison. Here's the "official" models available from nVidia with the fps in Batman AC as per the linked site.