Is there a way to show the speed of copying files on a Mac?
If you're comfortable in the Terminal, you can use rsync to copy some files from one place to another and it'll give you summary stats on the speed:

rsync -a --progress --stats --human-readable path_to_source path_to_dest


E.g. rsync --stats --human-readable ~/Desktop/Large-File /Volumes/OtherDisk/Dir

You can also type into the terminal just the command:

rsync -a --progress --stats --human-readable 


(note there needs to be one or more spaces after --human-readable to end that command and break before the source and destination file names are provided) 

Then drag the file / folder you wish to copy and drop it onto the terminal window, followed by dragging and dropping the destination directory. Dragging and dropping a file / folder onto a terminal window will place that file/folder's path into the terminal window. Dragging a file is preferred in most cases since it will handle a space in any folder or file name. In this case the space needs an \ to indicate not to end the file name exactly opposite of needing the space earlier.

The output of the above command will be similar to:

[jnet@Kyle ~]$ rsync -a --progress --stats --human-readable /Users/jnet/Pictures/Screen\ Caps /Volumes/Scratch 
building file list ... 
644 files to consider
Screen Caps/
Screen Caps/.DS_Store
      21.51K 100%    0.00kB/s    0:00:00 (xfer#1, to-check=642/644)
Screen Caps/Can someone downvote me please.pdf
      78.19K 100%    8.29MB/s    0:00:00 (xfer#2, to-check=641/644)
Screen Caps/Can someone downvote me please.png
     399.61K 100%   14.66MB/s    0:00:00 (xfer#3, to-check=640/644)
Screen Caps/ChefVMMemtest.png
       8.29K 100%  207.68kB/s    0:00:00 (xfer#4, to-check=639/644)
[...]
Number of files: 644
Number of files transferred: 638
Total file size: 176.85M bytes
Total transferred file size: 176.85M bytes
Literal data: 176.85M bytes
Matched data: 0 bytes
File list size: 12574
File list generation time: 0.002 seconds
File list transfer time: 0.000 seconds
Total bytes sent: 176.92M
Total bytes received: 14.09K

sent 176.92M bytes  received 14.09K bytes  14.15M bytes/sec
total size is 176.85M  speedup is 1.00