How much more power does it give? Does it make sense to spend 100 bucks more, or is 2.7GHz enough? I want to use it for work, but occasionally to cut/edit videos, record music, photo editing. For what use cases are the 2.9GHz and 3.1GHz processors, anyway? And what about the SDRAM, can I upgrade that myself? I could do that with the 2011 MacBook Pro. Thanks for your answers!