Mine were set at 70-ish inches and I haven't had any problems after adding wheel-weights. Before that the backend would occasionally get a bit light with just the 805 loader on the front when going down an incline (mowing in an Alabama ditch). Not sure I've ever had lateral stability issues..... though other than mowing along the road in the ditches I'm generally not working on slopes either.
Personally the biggest reason I like having it at that width is it allows 6ft implements to fully cover the tire tracks - though the tractor can handle a 1000lb 7ft disk harrow (on level ground at least) without an issue, and the 6ft box blade I have has almost been too easy to pull at times (even when full/overflowing).