There are only GSA-4163B and GSA-5163D. I don't know why but LG sells their external versions as GSA-5120D, GSA-5160D, and GSA-5163D. For US$120 or so, and if there isn't any drive that offers more for less, it seems it's the best choice for you. And since you already have NEC 16x, the lacking media compatibility with some types of media, it's not much of a problem. I personally burn most things on either GSA-5163D. DW1620 quality and speed are just as good but I use DW1620 specially for scanning writing quality.
BTW, if you know how to use an external case for HDDs and ODDs, buying a GSA-4163B bulk drive and a USB/IEEE 1394 box separately could be both cheaper and better. In my case, I got one without paying since it was a test unit but I never bought an external drive unless the price is nearly the same as the internal version like when I bought a Buffalo box with a Toshiba SD-R5002 inside from a Tokyo shop.