I know a bit about this stuff as regards c++ programming. Your always better off with less but more powerful cores, but there is a limit to how fast you can make a single core go.
As regards your question, its not easy. You have to break down your main loop into multiple threads, and work out where the critical points are that will force hold ups in the code. Personally I think 4 cores will remain the optimal amount despite the new consoles having more.