As an owner and user of a quad core computer I can tell you that copying multiple files in seperate copying operations is not sped up by using a multi-core cpu
The issue is that often the files you want to copy at the same time are either on the same physical hard drive or going to the same physical hard drive and trying to do two operations at once that access the same drive at one of both ends of a copy operation slows things dramatically.
However if you are copying two multi-Gigabyte files at the same time when neither files is on the same source drive OR on the same destination drive there is no perceptable difference in copy speed between doing a single copy and a double copy at the same time.
Unfortunatly this presumes that you have a computer with multiple
cores and atleast four physical hard drives (OR SSD)
Involve any of the four drives in more than one silmutaneous operation and it all slows way down.
I tend to do an awful lot of "serial" copies where I use an old DOS based file management program to copy files either by single point to point copying, "mirroring" directories, or "Alt-copying" large groups of "tagged" files
(either manually tagged or tagged by file extension, file location or attributes)
It's kinda neat to watch 210gb of mp3 and jpg files go from one drive to another in about half of the time I could have moved them using Windows Explorer.
PArticularly when I can copy them all "in path" with the directory file/folder "Tree" structure intact.