I myself do not know the exact percentage. I use Serato's Pitch-N-Time for other tasks and it is very high quality, I just don't know that I would want to use it when changing it other ways might be more transparent. Then again I have only done it using the "header" change Roger suggested so I can not speak from experience about the difference doing it it with Pitch-N-Time. Either way, good luck and let us know what you find.
_________________________
Chris R. Gibson
aka Loopy C
Micworks Ken Tamplin Mastering