As I currently own both machines I can say that the 8core is not that much faster at rendering, certainly not double. It might be twice as fast at encoding with multiple compressor instances running though. Also having 16GB RAM is most certainly overkill and would not speed up FCP if that were all that was running. FCP probably would stop seeing gains at 6GB or so (being that some of that RAM is going to system. With AE, PS, the rest of the FCS suite running you would still be hard pressed to max out 16GB. When Jaguar rolls around though – who knows.