Not sure if the following is of any help, but I thought I'd contribute since no-one else has. I'm afraid it doesn't come from any certification flight test experience - any flight test experience I have is experimental in nature and on rotary-wing types.
Sharp stalls usually start at the leading edge. Gradual stalls start at the trailing edge. Thick blunt-nosed sections are generally good for trailing edge separations (ie gradual stall characteristics).
Wing-drop with power on I'd surmise happens because of propeller wake-induced changes to the local angle of attack on the wing, higher on one side than the other. Given the nature of the propeller wake, this is probably confined to the inboard sections, so that's perhaps where a solution should be focussed, rather than towards the tips - I'm not sure though.
Lower Vso could come from a higher Clmax. Drooping the leading edge can give this, but it can do nothing to improve sudden onset of stall, just give you a higher Clmax (I think this is effectively what you see on the underside of the Bulldog wing, there's a crease near the leading edge which looks as if it contributes a gentle 'droop' shape).
On the PA38, versions equipped with four 'flow strips' as opposed to two (they're toblerone-shaped, about 1cm high and are about 15-20cm long) have a 3 kt higher stall speed, and in my experience will still tend to drop a wing power-on, although not by 60 deg.
A good book (although quite difficult to get) is Fluid-Dynamic Lift by S. F. Hoerner. It was privately published in 1975, there's no ISBN number on the copy I have, but Ch. 4 deals with stall characteristics of airfoil sections.
Apologies in advance if this is of no help.