I currently have a late-2007 MacBook 2.2Ghz, and I am looking to upgrade to one of the new models, but i'm just not sure which model to go for. Is the difference in price between the high-end MacBook and low-end MacBook Pro justified? Screen size isn't of major importance to me, although I would prefer the 15", but it's like a 55/45 split between the 2. Any advice would be much appreciated. Thanks.