Very Strange Problems-Software?Hardware?

i thought i encountered very strange problems with 812s.
kprobe 2.1.0 cd-dvd speed 3.00

Just hours ago, i burnt several dvd+r. But i found nero cd speed can not run any test at these disc; while they can be read at normal speed.
Then i use kprobe to scan them. The first disc seem to be very good at max speed. While others can only perform well under 2x-4x. (2x for disc starting, 4x for disc ending) . I can hardly understand this. Since I remember my first 5 discs performs great under max speed. (When i first sensed this, i though the burner went bad and changed for a new one)
Just now i suddenly found that nero cd-dvd speed began to work…

And i wonder whether us0j or us0n is better. tdk+rw(mcc a01) performs extremely poor with us0n. While i’ve no sparing dvd-burner as a standard tester.