If that is the device for your DVD drive, then this is probably the
cause of your problem. The correct mode is UDMA4. Check the
DMA settings again after you re-boot.
The LG version of this drive comes with a new IDE cable. Is there a new cable supplied with the Memorex drive? If so, you should use the new cable.
Assuming it is a flat ribbon cable, you can count the wires.
It seems that you already know how to save a PNG image of CD-DVD Speed scans. PNG is the best format to use, so you don't need to change anything.
I think your TRT is for a CD rather than a DVD. 8x is very slow and the fact that the end speed is lower than the start speed would indicate that something is wrong.