Some great stuff coming back on this thread, esp. the stall numbers from
the Italian Stallion (we will be in Tuscany next month!). But just
focusing on wing strength for a moment, what is wrong with my logic that
the relevant load that can be supported to structural failure is TWICE
the breaking load on one wing, with an adjustment for the net
lift/weight of the wings themselves?

Considering the effect of higher GW on stall speeds and various
scenarios, stall is certainly the overriding factor. Nonetheless, we
rated our IV-T to 4,000#, and consider it critical to know everything we
can about characteristics above 3,200#. To me, the GW rating of 4,000#
just means we have determined it is reasonably flyable up to that weight
(ie, still in CG). Unlike the GW ratings for certified aircraft, it does
not mean it is generally safe up to that weight, or that it flies the
same at that weight as at 3,200#. It is not a general purpose GW. We put
such admonishments in our POH, and hope to have pages of data to allow
any pilot who might fly it to consider what he/she is getting into if
they decide to venture up into those GW's. Any pilot flying one of these
planes should be able to understand the consequences and do the numbers.
After all, there are pilots making ferry flights every month at
ridiculous GW's. The ones that don't make it are almost always a
casualty of fuel starvation, not stall speed.

Brian Barbata