I have had both of these drives. With the current firmware available I prefer the BenQ 1620.
Your question - The 1620 will rip a pressed DL movie at 8X. The 3500 with riplock removed will rip the same movie at 7X.
On the negative side, the NEC will read a burned DVD+R or a DVD-R at 16X. The 1620 will only do 8X.