The Angelbird PX1 arrived a lot sooner than expected... nicely built card with a lot of attention to detail. Even includes actually useable printed instructions for assembly and an allen key for the screws. Some may find the white LED lights of the card an issue, but whatever - it's inside my case and couldn't care less.
Quick specs with an EVO 970 1TB NVMe installed in Angelbird PX1:
In slot 3 as an external drive with nothing on it and formatted HFS+, 1430 MB/s write & 1508 MB/s read.
In slot 2 as system drive (direct system drive clone with CCC) and formatted HFS+, 1302 MB/s write & 1401 MB/s read.
AJA System Test and Blackmagic Speed Test are basically the same readings. In case anyone is really needing more detail: Slot 1 was GTX 1080 FE and slot 4 was a USB card.
Took no more than an hour for PX1 setup, install to slot 3, format HFS+, clone system drive to PX1/EVO970, shutdown, move to slot 2, reboot. NVMe was immediately recognized as system drive and no boot issues. On 140.0.0.0.0 firmware in 10.13.6 build 17G65.
Previous system drive was Samsung SATA SSD (EVO 850 or 860) connected via Apricorn Velocity Solo X2. Velocity Duo X2 with same SATA SSDs average 450 MB/s write & 480 MB/s read as an external drive.
Was not the original plan, but may hold onto the Angelbird PX1 for system drive and wait until either the SYBA SI-PEX40129 or High Point SSD7101A drop in price before upgrading some media drives to NVMe.
Edit: Spotlight must have finished it's thing. Now reporting 1448 MB/s write and 1509 MB/s read in slot 2 with same tests.