Hey, I ended up getting the BenQ 1650 based on the asumption that it would be as good as the 1640. It depends what you want in a burner. Each has good and bad parts. I wanted a burner for doing Dual Layer backups, that wouldnt take forever. The 1640 can do dual layer burns in 16 mins. It's also able to write 2,4x Verbatim DL dvds at 8x. Unfortunatly, due to the piece of crap computer I am using, a pentium 3, 256 ram, etc, I am unable to burn at 8x even with the program that lets you adjust the write stratedgies of the Benq drive. Others have been succeful though. The long story short is that no drive at present, straight out of the box, is able to write 2,4x DL dvd;s at 8x speed like the 1640. There are drives that can write those Verbatim 2,4x dvd;s at 4x though. My sony DRX-800UL does it, but gives me Quality score results on Nero cd/dvd speed of 70% as opposed to 93% when writing at that rated 2.4x speed of the media. Overall, just have a look around at the reviews, and see what the overall scans look like for the different media types.
If you have a computer with around 512 ram, a pentium 4 processor, and an internal hard disk that runs at 7200 rpm the I dont see why you shouldnt be able to get yours to write using the 8x write stratedgy.