The general consensus of opinion is that you get fewer errors by not burning at maximum speed. Most of us have settled on 8x or 12x for 16x media, depending on the quality of the disks. Better quality, like MCC0004 Verbatim, can normally be burned at 12x. I personally tend to use 8x for all my single layer dvd burns.
There are certain types of 8x media, like Taiyo Yuden T02 +R 8x, or Verbatim 8x that can be burned at their rated speed with no ill effects.