I'm planning to get a new 5K retina iMac (for photographic editing, web development and some video editing) and I think I'll opt for the 1TB SSD storage, since that seems to be the speediest option. However I can see myself running out of space at some point, so I'll be needing some sort of external storage. What would be the best option for external storage in terms of speed? Thunderbolt SSD? Or some sort of NAS? Perhaps different types would be preferable for different types of media?