CURLOPT_MAX_RECV_SPEED_LARGE is not supported for FILE:// transfers so the transfer is still made as fast as possible. Although after the transfer is completed, libcurl will still run it through the ordinary state machine where it will detect that it ran too fast and sleep until the average speed has gone down to the max speed!
This might also affect TFTP in a similar way, I haven't checked.
Reported by Mohammad_AlSaleh http://curl.haxx.se/mail/lib-2013-12/0053.html
Fixed in commit 2715d7f948c8e. The option not working for FILE:// is also documented now, since commit f718415bc791.