Its possibly its the blank media itself.
I have a 2 LG drives and have never experienced such issues with Verbatim or Memorex media. Never tried Ritex though.
Some drives can be picky when it comes to blank media.
Also, which software are you using to burn the discs?
Most have a option in the software itself to choose a write speed.
With Nero for example, the write speed option will be after you complie everything, and right before you start burning.
In Advanced options.

So whatever app you use, it should be something quite similar.
If the current software is set to Auto, it should go by whatever the media is capable of and burn as fast as it can.