I do have an Rpi3. I do as well have an SSD laying around. Just need to figure out, how to deal with it… ie, set the SSD to boot, clone the SD card etc… I´m no good at Linux, so things like these are taking quite some time, unfortunatly.
It’s easy, not much Linux involved.
Set SD Card to enable USB boot, no need to prepare the USB drive, this is done with the imaging later:
Then i used win32diskimager to create an image of the sd card and wrote that image to my usb hdd. (Etcher works similar, i guess.)