I've been doing wonderful burns (very good results with kprobe) with my 451@832 (CG3E firmware), at any speed, but the greatest results where obtained with +r media @8x, so I always use this writing speed.
In my last 2-3 burns there's a little-big problem: when nero it's burning (data or video dvd) my pc slows down too much, I can do anything but watching nero... Moreover the driver goes about 3-4 times in buffer underrun! Btw the results are still very good... I experienced this problem with various kind of media: ritek, ricoh and mcc... The problem persists!
I checked if my hard disk and drives are in udma mode, and they are! The hd is in udma mode 5 and the 451@832 is in udma 2...
Where can be the problem? Tell me it's just a windzoz problem! I'll try to burn a dvd under linux if necessary!