Any mobile graphics card is weaker than its desktop counterpart. You want a better card than a 9400m for gaming -- the 9400m is an integrated graphic solution and weaker than almost any discrete graphics card.
For some reviews of mobile graphics cards you might consider checking out notebookcheck.net
That said, if you already have the macbook I would go ahead and try other similar games with similar system requirements on it to see how they perform. (demos provide a free way to test your system)