[garthk]

For those still not quite getting it:

The first copy to RAM was a sequential image copy, thus not bottlenecked on seeks despite spinning platters.

The second copy from RAM was a file copy with a lot of random I/O, but not bottlenecked on seeks because it was reading from RAM.

Bulk writes tend to be more efficient. They might have made temporary configuration changes to make that end faster, or not if they lacked the appetite for the extra risk.