I have ordered a MacBook Pro and am hoping it comes with 10.9. If it comes with 10.10, what is the best way to get it back to 10.9? I have another Mac running 10.9 that I can use to get 10.9 onto an external drive. I also have a 10.9 installer that was downloaded from the App Store the day before Yosemite was released. I don't really know if it installs 10.9 or 10.9.5.