What i've noticed about the buffer in nero is that it drops and comes back to the middle. The buffer reading isn't stable
There are 2 buffers, we need to know what each is doing.
The burn speed graph looks very much like the drive is in PIO. Suggest you uninstall the IDE controller and reboot, then re-confirm that ALL drives are actually running in UDMA status, not just set to DMA.
Also, run a transfer rate test in CDSpeed to see if the drive can read at full speed.