Hi people! My 2013 rMBP 13" is still running OS 10.9.5. I fear the newer versions are less optimised/heavier for my ageing laptop, and I don't want to lose performance. I'm very satisfied with the machine right now! Unfortunately it is getting increasingly difficult to stay on OS 10.9, because of apps that don't support it. What should I expect if I update to a newer version? Thanks a lot!