Soon I'm going to upgrade to the new 27" iMac - either the mid - 256gb SSD, mid - 512gb SSD or top - 512gb SSD. Currently I have a 2011 27 iMac with the OS and apps on an external SSD and my home directory on the internal 3tb hard drive. How would I go about merging that setup? ie. OS, apps and home directory on the internal 256/512gb SSD. As I've got pretty much all of the current home directory synced with Dropbox (~700gb), I would need to do a selective sync and start moving some data over to an external drive.