My late 2013 iMac (i5) is plenty fast for most of my needs. 1TB HDD. I wanted FD but the dealer didn't carry that model. Am I opening a can of worms to think about an ext SSD such as the OWC elegato? This would be for the OS and applications only. Some background: I always put my computer to sleep instead of powering down. Startup time isn't an issue. Favorite application is Aperture.