First of all, it is unlikely any quality disk you burn will be a coaster straight from the burner when burnt at its rated speed. (overspeeding is a different matter)
However, that doesn't mean the disk does not have any errors on it. It is basicly impossible to write a disk with absolutely no errors on it, and it is equally impossible for a read head NOT to introduce errors of its own on readback. This is not a problem because the drive will automaticly correct these minor errors. (and does so, without the user ever knowing normally)
Secondly, if you set the priority of nero cdspeed to high (using task manager), and press start, and actually LET it finish reading the entire disk, you should get an almost perfectly straight line left to right on the read graph. Tiny glitches can be ignored, as they are likely due to timing rather then disk problems. If there are serious slowdowns on the Pioneer 107D while reading the disk at 8x, you should consider reburning the disk. If there are actual unrecoverable errors, you will get an error message in a dialog with "UNRECOVERABLE ECC ERROR" or something similar.
As for data corruption, that isn't going to happen on a normally burnt disk unless your processor/memory or motherboard is broken. The DVD stores data with a lot of extra error correction information, and your average DVD will require the use of this error correction hundreds of times a second during DVD access. If the error correction cannot handle the error rate from a particular disk, it will not silently corrupt your data (unless you specificly ask), it will return an UNRECOVERABLE ECC ERROR. Data is also protected from the disk controller over the cables to the drive, because the cables also use ECC to verify the data is being sent to the drive correctly. ECC is also used when reading data from the hard drive into memory.
So any DVD you burn that reads back properly, will have 100% of your data on the disk.