The main difference is in the GPU. The 2.4 GHz model has a GPU that is a step up from the 2.2 model. The GPU also has double the RAM on it, which should give a solid boost in gaming and make it a much more future-proofed GPU.
In terms of regular use, if you're not a gamer or use software that highly utilizes the GPU, you would be better off with the 2.2 GHz model.