Quantifying Vso, Va, TODR etc. at various weights is all useful stuff, but not what I am after.
The authorities consider 10% overweight safe enough that permission is granted without formality, other than notification. They hedge that permission with enough restriction to make it useful only for ferrying.
At which point does it become unsafe, and how do we quantify it?.
It all seems a bit of an "angels on a pinhead" argument anyway. I say this simply because, as far as I can tell, MAUW in light aircraft is a function more of TO/LDR and Vso needing to be =< 61kts rather than structural considerations.
With regard to insurance, quoting a case where the insurer failed to pick up the tab because of an unqualified PIC, does not translate directly to the overweight case. My policies, at least, specifically require either me, or a qualified pilot, to be IC. In the event that an unqualified pilot was at the controls at the time of an incident, I would not expect them to pay. However, the only clauses which could be interpreted as pertaining to operating within the bounds of the ANO, POH etc. refer specifically to conducting the flight in a "safe" manner, and not in a narrowly drawn "legal" manner.
IMHO some data concerning insurance claims denied as a result of overweight operation would help.