Assuming your hardware meets system requirements: http://www.mathworks.com/support/sysreq/current_release/index.html
Then I would expect 4 cores with 4 workers to outperform 2 with 2 during the parallel portion of your code, assuming equivalent clock speed. However there may be some other differences in performance on AMD vs Intel due to things like different underlying libraries etc. I'm not sure, don't know much about that comparison myself. Also keep in mind that's assuming we're discussing PHYSICAL cores, not virtual, as you should avoid running more than 1 worker per physical core.
