From my experience at "deterrrent buffet levels" there is zero incentive to fly any slower. Severe vertical and lateral shaking of the flight deck would be typical.
Clearly this is a qualitative assessment made by experienced TP's.
Also just because the stall has been defined in this way it doesn't necessarily mean that "dangerous characteristics" will be encountered at higher alpha.
Surprisingly deterrent buffet levels may not necessarily be a structural consideration.
One type I flew could suffer structural damage to the stab with no stall buffet noticeable to the crew. The stab was always instrumented for structural loads prior to stall tests. This was despite the flaps up stall being defined by deterrent buffet.
It would seem that deterrent buffet levels are pretty well always a stall handling issue - I personally never encountered it being an issue during stall speed determination. Would be an interesting horse trading exercise to argue deterrent buffet verses the need to achieve a particular stall speed.
Stall buffet levels seem to be typically low in the configurations where stall speed is an important performance consideration.