Got the drive, used Solidigm Storage Tool 1.13 on a Windows box to update the firmware to 5CV10302 (not sure if that matters at all, but I always update firmware to the latest), took it home, put it in the Sonnet Echo Express SE IIIe that I already own (on a "dumb" StarTech card that simply maps the signals on the U.2 connector to a PCIe x4 connector), hooked it to my M2 Max Mac Studio, formatted it APFS named "One Disk To Rule Them All" (you have to have fun; I won't leave it like that), and proceeded to test.
First thing I did was copy a folder of JPEGs and NEFs (Nikon raw files) from the internal boot drive to the Solidigm. The folder was 151GB and it copied in 63s, meaning 2.4GB/s. There did not seem to be any visual slowdown at any part of the copy, meaning (to me at least) that there is no cache filling up and then the copy slows down after that, such as what I observed on a Samsung 8TB QLC SATA drive a while back. Then I rebooted the computer (to make sure no files were cached anywhere) and did the same copy in reverse, to measure the read speed of the drive. Exactly the same time: 63s. So I'm guessing that both read and write are limited by the speed of Thunderbolt. But I couldn't care less: to me, this is absolutely fantastic speed, and more than fast enough!
Below are the results from Black Magic and AJA. Both matched my measured speed exactly for write, but read was oddly a little less in both.
Now I'll just leave the computer overnight to see if it manages not to panic. If not, I think this drive is officially what I've been looking for for a long time.