First start by reading this very well written article that explains all one needs to know in simple terms. SSDs, Sata I, II, III hard drives, flash drives, thumb drives and SD cards are all discussed. In short lets follow the data flow. The SLOWEST part is what YOU need to address – lets discuss all the parts
a) bus speed – so USB 2, eSATA, 3.0, thunderbolt, 3.1, thunderbolt 2 and thunderbolt 3 are IN ORDER the slowest to fastest. (usb 3 vs thunderbolt 2) This is talking about the computer that one plugs things into. (I might have the order slightly off – so comment if I do) …
b) the circuitry between the final storage and the final device is next
- SATA drive?
- USB Stick – USB circuitry
- Flash Drive – circuitry
- etc
c) the device itself has a write speed. If you use a SATA III hard drive that has platters it will be much slower than an SSD. A usb flash drive is different than a USB 2.0 drive etc. or an SD card
So that I really want for Christmas is not available yet. HOWEVER, my next favourite is a thunderbolt 2 external dual drive bay by Starch and then add SSDs, but this is a $300+ experiment not including hard drives so likely this will all be theoretical for now. The reality is an SSD in a USB 3.1 case with good throughput will get one by. You can find a few USB 3.1 hard drive cases for <$30 CDN.
Next understanding how to copy a hard drive quickly means a drive duplicator. I have a VERY old one by Byttec and I love it but it takes 4-5 hours to copy a 1GB hard drive but it works. If you use a USB to USB copy – the data copies through the CPU or hopefully a bus (mac) but all this needs to be known to make the best choice of a final purchase.