I'm considering buying one of the new 13" rMBP's, but I'm wondering about the battery life improvement claim. They say that the battery life went from 7 to 9 hours, but I would expect that the previous 2012 13" rMBP's battery life would increase by at least an hour if it were upgraded to Mavericks. Yes/no/maybe? I'm wondering if it's worth it to get the new one or if I should just get a better spec'd refurbed 2012 model for less. Thanks for any insights.