My setup was a 1620 (47L9) in a Prolific PL-3507 equipped case. The BEST I could do was 15.50X and right at the end the buffer would start going up & down. The last 5% of the burn I started to see reported error (PO/PI) go up.
My burst rate was 24 MB/s.
I have chosen to use the B7U9 firmware @ 12X with a 21MB/s burst rate. I get a far better quaility scan and my burn time is only 6:15.
So for what it worth, same burn time (+/- 10%), better quaility score, no large PIF at the end. I PREFER B7U9 AND FORGOT ABOUT 16X !!!!!