I have a 2009 MBP, and it needs replacement. Debating between a 2015 (for retina, etc) with all types of external drives, or a 2012, removing the optical and configuring some serious, internal storage. As far as I can tell, performance should be good enough for me in terms of processor and memory. My one question -- how far back will they support the hardware with new OS releases. This is a bit like predicting the future, of course, but what is their track record currently? I think they started dropping support for some '08 models. Can I get another 6-7 years of OS support out of a 2012 model design??