I recently bought both the Benq 1620 Pro and the LG GSA-4163.
After upgrading the LG to the latest A104 firmware, i've noticed that the RW's i've been using work quite well. Also some of the cheaper media, SKC & OPTODISC DVD-R's have worked a bit better than either my old Liteon or the Benq.
The Benq has written other 4x DVD+R's i have at faster speeds so is quite useful in that regard. Although, to get good performance out of the -R's, i've had to use B7T9 and to get good performance out of the +RW's, i've had to use B7U9.
I don't believe one should have to keep flashing firmwares like this for different media. B7V9 is no good for either of them and could only imagine using that for +R's and better quality media.
The downside to the LG is no bitsetting on +RW's and no Disc Quality scanning, which where the Benq comes in useful!