It's possible that burning at 4x, depending on your media and your burner/firmware will give better results. The opposite is also possible, or there may be virtually no difference in the burns.
MCC is Mitsubishi Chemical Corporation who make dye types for dvd's. Not all MCC is genuine made by Mitsubishi, but Verbatim ones are. If you get cd-dvd speed, it will show you a manufacturers identification code that gives you some idea of who made the disk.
The pearl whites I think might be made by Ritek (without checking), and are not thought of very highly. Can't confirm what they look like, but others can.
If you get cd-dvd speed (It's in Nero toolkit btw but you can download and replace it with a newer version easily, just google it and overwrite the old one with it) you will be able to check your disks to see how your burns are at 4x and 8x speed, as well as test them periodicaly to see if the data is still intact. If you're getting good burns at 8x, then stick to that speed.
Peoples opinions of the verify function vary, with some saying it misses stuff, and others saying it's too picky. I don't use it much, but perhaps on a special burn. You can use the Transfer Rate test and Quality Test from cd-dvd speed to test how well the information can be read from the disk and how well the drive can read the disk respectively.
What these tests can read and how accurate they are is VERY dependant upon your burner! What make and model do you have again?
The above is a bit simplified and general, but you can read more about these things in the Blank Media section of this forum.