Just coming back to share my results. Booting the latest Ventura from the drive on Thunderbolt, I'm getting 2,300 MB/s read and write. It's like @siclark said, it's pretty much a brand new machine. (For comparison, I'm getting about 1,200 on a base 2020 MacBook Pro.) All in, about US$160.
Thanks again to @siclark for the tip.