Transcription vs. Free writing

This is an update to my earlier post (http://www.classroom20.com/forum/topics/typing-speed) on typing instruction and CCSS.

As I am researching typing instruction I am wondering if any of you may have seen or have any research on the difference in typing speeds when students free type (write an essay from memory) vs. transcribing/copying a passage.  I believe there is a difference in speed but would like some research to back up my theory.  Also do any of you know or have suggestions on how to help increase typing speed while free writing?