I have a late 2007 2.4ghz iMac and a 2008 Unibody Macbook which is also 2.4ghz. I would like to replace them both. I am looking at the retina Pros, and have narrowed the choices between the high end 13 and low end 15. Screen wise isn't a problem as I have a 21" LG monitor I can hook it up to. This way I can consolidate everything into just one computer. In your opinion, is the extra money for the basic 15 worth it?