I is more dependant on your hardware then software. As long as your burner has the overburn feature then you will be ok. Most software already suuport this feature. I would say that anything less than 4X won't be able to do this.
It's both, but since all the major burning software packages have supported 80-minute/700MB discs for the past few years, it really only comes down to hardware now.
Overburning has nothing to do with it. Use of an 80-min/700MB disc does not constitute overburning, unless you attempt to record in excess of its rated capacity.
I have an ancient Sony 928E (2x0x8) that can easily record on 80-minute media, so rated burnspeed is not a determining factor, and that drive is not capable of overburning.
Unfortunately for you, unless another user of the 6206A can step forward to confirm one way or the other, you have no other alternative but to try one. They're common now, and relatively cheap. Buy one, and if it works (even for use as a 74-min/650MB disc) then you'll know you can use them. Sometimes there is some very good deals available on 100-disc spindles of 700's, so being able to use them -- even as 650's if the burner won't do the last 50MB -- could be a good thing.