I was having this same problem with my LH-20A1H and Benq DW-1655 drives. I found, and deleted, a driver that was left over from some software I had tried and uninstalled it and it solved my problem.
Check in your Windows/System32/Drivers folder for a driver named SPTD and see if you have it. My burst speed went from 20 to 35-40 MB/s for my LiteOn drive and from 18 to 24 MB/s for my Benq after I got rid of it.
Heres a link that may help:
This may not help your problem, but it helped mine and I thought I would share it.