We are building an application that uses AERender.exe on the command line to output an .mp4 file.
Due to what licenses we have available, we're creating the project file using CS5.5, but rendering on a server using CS6.
Will there be any noticable performance decrease from opening a CS5.5 project in CS6?
I would think that would depend on the project, plug-ins used and other factors. You will probably have to run some tests and graph the results.
Theoretically, the answer is "not much difference", but I would go with Rick's advice of running some tests to be sure.