Yep, a SATA SSD that runs over USB 3.0 is very fast on the RPi4, as long as you make sure "UASP mode" is enabled (this can take bit of tinkering). You don't even need external power, just a $5 USB to SATA cable.
I use a combination of official RPi 4 power supplies and an Anker 6-port USB power block that I'm pretty sure tops out at less than 3 amps.
More importantly, everything is plugged into APC UPSes.
However some USB SATA IC's have issued with it on Raspnberry Pi[2], requiring one to disable UASP. I have some JMicron-based USB-SATA adapters which falls into this category.
[1]: https://www.jeffgeerling.com/blog/2020/uasp-makes-raspberry-...