I have done some rough rounding above, and took the time to write more accurate numbers.
The actual total is 49,436 items, totalling 244.9 MB. Copying all of this was going to take at least an hour.
And another copy was 8,082 items, totalling 76.0 MB, 8,081 items, totalling 72.6 MB, 13,825 items, totalling 9.1 MB, 13,825 items, totalling 9.1 MB, 2,068 items, totalling 29.0 MB, 3,555 items, totalling 49.1 MB. Copying these separately, yet concurrently took minutes.
Both of these were from the same SSD to the same usb stick.
Regarding the large files
4,127 items, totalling 43.1 GB took more than 8 hours
Another non-concurrent batch copy of 73 items, totalling 725.5 MB, 163 items, totalling 1.4 GB, 1,332 items, totalling 13.0 GB, 721 items, totalling 8.9 GB, 507 items, totalling 7.1 GB, 27 items, totalling 476.6 MB, 17 items, totalling 456.7 MB, 15 items, totalling 409.1 MB, and 1,272 items, totalling 10.6 GB took under an hour.
But actually, that was hard drive to sd card vs usb to hard drive respectively. I stopped the single copy operation containing all from usb to hard drive because it was estimating too long and I remembered the trick using the small files.
totalling: spelling error in Files.