I am about to become a first-time Mac owner, and am debating between the 13" and 15" MacBook Pro. I know that, in general, 13" wins for portability, and 15" for utility with juggling multiple windows (I am a mega-multitasker). What I am unsure of is performance differences. I can configure both sizes to have 320 GB storage and 4 GB RAM. Same on paper, but will performance be different between the two models? Will either get significantly hotter with a given processor, will it drain the battery on the 13" faster to have more RAM? Advice?