I have a success rate of 2 out of 3 using DW1650. I have only used Memorex 2.4x DL media so far.
I have used ImgBurn 22.214.171.124 for all the burns.
Initially I had setup the 1650 in a ADS Pyro Firewire/USB2.0 enclosure. Single layer DVD burned fine, but my first DL burn (Memorex 2.4x) failed while trying to write the 2nd layer. Unfortunately I didn't save the log.
Now I have the 1650 as secondry master and I got successful burns for 2 Memorex 2.4x DL media. I didn't see anything different for the burner buffer between Pyro Firewire and IDE connections. So I don't know whether the burn failed because of the external enclosure or bad media.
I also noticed that Qsuite 2.1 QScan was throughing an error when the drive was connected via Firewire, but no error when using the IDE connection.
QScan says both the Memorex 2.4x and Verbatim 2.4x DL media to be not safe for burns using 2.4x speed. I get a big spike for TE and FE when the layer changes.
Both of my Memorex 2.4x DL got 79-80 quality score using 1650 and only 43 when using Lite-On DVD-ROM.
All of my Iso images are created using DVD Decrypter and Lite-On DVD-ROM.