Good Lord, a 100-pack of DVD+RW
The W11 are very good, congratulations.
The "slow-downs" are by designs as it apparently is not the same technique to reach 16X as in the transfer rate test where you start at a constant angullar velocity to reach 16X at the outer part.
Here speed is increased by steps.
My 2 cents;
Hopefully Erik Deppe will kick in for a more substantial explanation.