Hi, I recently bought an NEC 2510a and had been wondering which 8X media to use with it as well. I can tell you what NOT to use. Just for the heck of it, I went to ecost.com and picked up a 25-spindle of their 8X Promedia (Lead Data) DVD+R disks, which cost around $12 for the spindle after mail-in rebate. Now, from what I've heard, these disks are no different than Sony disks and are in fact manufactured for Sony by Lead Data.
Sadly, even though these disks are rated for 8X, neither Nero 6 or Roxio Easy Media Creator 7 coupled with my 2510a have been able to write to these disks any faster than 4X. Neither program offers an option to even select 8X with this media.
At first, I thought maybe updating the firmware would allow my 2510a to write to these disks at 8X like they are designed to be written to, so I went ahead and updated the firmware from 2.15 (which is what it came with) to 2.16... but still no dice. My burner still won't write to this brand of media any faster than 4X, no matter which burning program I use. So based on this experience, I would have to advise anyone wishing to burn at 8X to stay away from Promedia/Lead Data disks. However, when burned at 4X these disks seem to play back well on the Panasonic DVD-F85 player which I have connected to my TV... although this particular player was designed with DVD+/-R disk playback in mind, so I can't exactly vouch as to how well the disks would play back on slightly older DVD players
In reading, someone else in this forum had mentioned that they use their 2510a along with Prodisc 8X DVD-R disks and have had great success, so I think that I will give Prodisc a try once I use up this spindle.
Tim