I'm still using Mavericks on my Retina 13. I usually use it with a 27" 2560x1440. I was having problems with my iPhone 4 syncing with iTunes 11. I called tech support and during the process they had me upgrade to iTunes 12. iTunes 12 is unreadable. It looks OK on the Retina screen, but it's almost painful to try to use on the external. The text is tiny and everything is too white. When I set the text size to large, it just adds more white space around the same tiny text! I can't skim through lists of songs and podcasts, I have to pick one line and concentrate to read it. What don't they offer a bigger font? I heard about legibility problems with Yosemite. I'm worried that if I upgrade my OS everything will look like this. Do the legibility problems from Yosemite get better with Mavericks? I'm also afraid to upgrade to Safari 9 on Mavericks. It almost seems like they're sabotaging legibility on standard screens to help sell Retinas, but what is the point of that when external Retina screens are neither available nor supported?