The QNAP TVS-472XT costs a bomb, but has a pair of Thunderbolt 3 ports and can take a GPU for faster media transcoding, and its operating system is probably the best in the NAS market. This NAS is mostly for video editors or small and mid-sized businesses that want a very reliable external storage device with tons of features and options.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips