They vary. I've had some 8X DVD+R Ritek R03 from Memorex that produce terrific burns on my PX712 and BenQ 1640. And bought at Wal-Mart, no less!
But since my previous burner was so picky about media, I assumed they would work as well with this new Plextor. Friends of mine who own older Plextor DVD burners use these Memorex as well, with positive results (but as you pointed out, that could be due to the fact there are 6 different types). I'll try picking up some better media tomorrow.
The older Plextors have different chipsets and hardware inside them, and also have more mature firmware than the 760 currently has. As time passes and you install newer firmwares, you may find burning quality gets a lot better down the road. Apparently my PX712 was underwhelming until firmware 1.04 when the scans for a lot of media improved dramatically. Sometimes the combination of a burner's burning hardware and the firmware produce great results on not-so-great media; might have been the case with your NEC. Generally speaking, my PX712 gets better results than my BenQ 1640 with lower quality media, although it's no better with the good stuff.
Also, I tried burning at a slower speed but it had the same results, garbage discs.
That was true during the old CD days with the dreaded buffer underruns, but my experience has been that DVD media burns best at the speed listed on the packaging.
Now, what are Sum-8 and Sum-1? I do not see them listed in PlexTools (I have Professional, not XL). And how do I know what a good and bad output graph looks like?
In the yellow area on the left of the Plextools screen, you should see something called Qcheck PI/PO Test. If you click it, the graph on the right will appear and a drop-down selector for SUM-1 or SUM-8 (and others) will appear. Each one will take 28mins :doh: to run, but should provide a rough predictor as to how well the media might play in your DVD player. More exact interpretation information is provided in the FAQ at the top of this forum, but for now the higher the numbers on the graph, the poorer the recording is. If the SUM-8 numbers exceed 280 and the SUM-1 graph shows values above 4, there's a possibility of getting corrupted playback on your DVD player.
Try it and let us know how it turned out.