Looking at getting a used mac for my wife. What are the primary differences between late 2013-late 2015 models? Trying to stay just under 1K if I can. I have heard the late 2013 are almost as fast as the newest models? Which older model from 2013 and up is a good match for price/performance? Which older ones still keep up with today somewhat? Mostly light graphic art stuff and maybe some light gaming. Thx in advance.