I agree with this assessment. Most of the cheap bulk CD discs that I use tend to burn notably cleaner at either 24X or 32X (as shown by CDSpeed). The time difference is only about 60 seconds or so.
The BenQ will likely burn your DVD discs a bit cleaner and faster than the NEC 3520 - especially when used with +R media. I have both BenQ 1620 and a NEC 3500, and the BenQ burn generally produces a cleaner CDSpeed scan - particularly when the burn is made at a speed faster than 8X. And most 8X +R media overspeeds perfectly to 12X when it's burned on the 1620.
The BenQ also offers you CDSpeed quality scanning while the NEC currently does not (although apparently this is now on the immediate horizon for NEC drives too).
Finally, with ala42's new read patched firmware installed, you'll be able to rip any pressed double-layer movie to your hard drive with DVD Decrypter in under 10:00, making the BenQ 1620 the fastest reader available!