I can't burn faster than 2.4X

[h00ti3]

I have a NEC DVD+RW ND-2100AD which is a 4X burner. 90% of the time, the maximum speed I can write is 2.4X. Every once in a while, a disc I use will write at 4X. Sometimes it will be disc 3 of 5 when I'm burning a series of discs all from the same spindell.

All of the discs I use are 8X:

Phillips DVD+R 1-8X
Maxell DVD+R up to 8X
Imation DVD+ 8X
Sony DVD+ 8X

Is there some firmware I need to upgrade? Is my drive defective? Are these DVD's just pos's?

[cynthia]

Used burning software?

[h00ti3]

Oh yeah, more info would be helpful.

Nero Version 6.3.1.6
Windows XP Pro
3.0GHz Pentium 4
1.0GB RAM