Why does my DVP1650T rip so slow?

Hi,

I have a Benq DVD-Rom DVP1650T and a EW164B flashed to DW1640.
If I copy a DVD to harddisc, the DW1640 is very fast. On single layer discs and DVD-R/DVD+R it read up to 16x. On dual layer up to 12x. On single layer it starts reading at 6.5x.
My DVP1650T is much slower. It starts reading at 3.5x and then goes up to 10x. No matter if single or dual layer.

Why is this?

The discs I tested are without any read errors. So this cant be the problem.

Firmware for DW1640 ist BSMB. Firmware for DVP1650T is A.FD.

Schrauber
Is good to be sure, about the DMA function is turned on.
Maybe Nero info tool, or other information software.

With DMA there is no problem. Drive is in Ultra DMA 4 mode.