It depends mainly on the writer, and the media.
Example: I have an older Lite-On that overburns everything I've ever wanted it to. I also have some media thats designated at 90/99 minute media. I have burned more then 90 minutes onto a disc with this combination, with a maximum around 95 - but could maybe do more. Unfortunetely 90/99 minute discs are near impossible to find anymore, so I use the last 50 stack I have sparringly. I still have a good 25+ left.