How fast is the internal PCIe SSD in the last 2013 MacBook Pro Retina 'Crystal Well? Fast.
The spikes are interesting behavior which might or might not mean something significant, such as performance when mostly full or after long term use.
A backup drive for travel is essential, but store it separately in case of theft of the laptop! The beauty of the OWC Mercury Envoy Pro EX is that it fits into the palm of my hand with or without its supplied soft cloth bag with short USB cable (powered from data cable alone). Which means it can go into most any pocket also or nook or cranny while traveling.