For DVD-9 I use DVD Shrink that is set to 4635 MB and burn the ISO with DVD Decrypter only to Plextor 716A on DVD+Rs. For DVD-5 I use other burners than do not support overburning.

Ben is right though about the problem at the outer part of a disk:
- On less quality media, the dye often not spreaded evenly to the outer part hence the quality of outer part is less than inner part.
- On high speed writing such as 12x or 16x the higher speed is reached at the outer part; this means the outer part will produce higher errors.

So to overcome this you need quality media and burn at rated speed or for 16x media burn at one tick lower (12x).