This is a frustrating topic to research and has become a bit of an argument among my videographer friends. My suggestion has been: keep your current project on the internal FAST SSD. Finish it. Save it to your external HDD. Surely editing video footage that's stored on the internal SSD will prove to be a faster experience than editing footage stored on an external HDD. The current SSD in the skylake iMac reads at nearly 2gb/s vs. an external hdd that reads at 230mb/s or less. But many insist you'll get faster performance by keeping all your footage on an external hdd. Just doesn't make sense to me. Now some say, if you use your internal drive with FCX the drive will fill up too quickly. But I'm suggesting you only keep your current project stored on the internal drive, nothing more. Not your iTunes library, nothing, just your current project. PS - if your projects are hollywood, yeah I'm sure they'll exceed the 1tb internal drive. So in that case, of course you need external, I get it Thanks!