Alright, finally got to do some bench marks for this computer.
Blackmagic Design v3.4.2 disk speed test (best of 3 runs, all conducted from Sequoia 15.5).
Original 256GB SSD: 510MB/s write - 1021MB/s read
Apple 655-1859H 512GB SSD: 1346MB/s write - 1384MB/s read
For the SSD, the 512GB drive has...