Hm. I missed this post before. Can you do some more tests to see if other media are burned with what result for "consistent" comparison. Every drive might behave a bit differently. (That's extremely true with Plextor PX-716A and PX-712A btw.)
CMC MAG AE1 is a very, very popular and widely used 8x DVD-R type of media, also easily and cheaply found in South Korea, not to mention the US, China, Europe, Japan, etc. Though it's also true there are some very poor-quality CMC MAG AE1 distributed somewhere. (Which is why one of South Korean media importers/resellers) have sold them at the lowest possible prices recently.)
RICOHJPNR02 should work beautifully by comparison. Whether Ricoh brand, Philips brand, Fuji brand, Memorex brand, LiteOn brand, RICOHJPNR01/R02 media work greatly because of wide availabiliity (for testing) and consistent quality.
If media quality varies a lot as with RITEKG05 and CMCMAGAE1, the drive manufacturers have bad lucks. Because after they wrote some write strategies in their firmware, some resellers and manufacturers might distribute media of much worse quality with the same media ID. It has happened very often.
Maybe you can do "Transfer Rate" tests of the CMCMAGAE1 disks on the GSA-4163B itself. I also did some TR tests especially on some problematic media like Princo 4x DVD-R and Gigastorage GSC001 media. (There are a lot of different Princo 4x DVD-R and Gigastorage GSC001 media, a very well-known problem since 2002 for GSC and Princo.)