Thanx for the explanation! I was wondering what Z-CLV means, now it makes sense. Also, I didn't know that it's possible to test the recording speed with CDspeed. I ran it and got the same exact graph.
However, the problem I'm having is something else, and as far as I can tell, is caused by Roxio. I've ran a few burns and now have a definite pattern. Basically, when the drive needs to switch from 16x to 20x, the activity light starts flashing, and the effective speed drops to 10x instead of increasing to 20x. When it gets to the point of switching to 24x, the activity light becomes solid again and the speed increases to 24x. So for some reason there's a problem with 20x speed. I'm wondering what flashing activity light supposed to indicate.
The strangest thing is, it only happens in Roxio, and only in Creator Classic. Disc Copier works fine, I observe speed inrease the way it's supposed to be. Also works fine with Nero 6 Express. No speed drops or activity light flashing.
I've updated Roxio 6 to whatever the latest rev is, no help. Has anyone seen this problem?