If the games that you will be running are designed to take full advantage of the multi-core processors, then I would recommend the Quad Core processor, since the more cores the processor has the more tasks the processor can perform at the exact same time.
If the processor is designed to run only in single core, then you might prefer a processor with higher clock speed like the i7-2620M.
In order to determine if the game is designed to take full advantage of multi-core processors, you need to contact the game developer.
