I always understood that the design landing limit equated to a touch down at 1000ft per/min at max weight + proof factor.
16.6 ft/s - I'd say that sounds about right for an extreme liimit
12~15 ft/s is normally what's quoted
The vertical speed and weight limits, are more a measure of the kinetic energy absorption of the u/c. beyond that G ^ rapidly and is not directly calculable
4g at 15 ft/s implies a very small deceleration displacement (6" to 9"), implying the u/c has already done the best it can and we are into plastic deformation territiry
Very surprised indeed if 4.6 G recorded and that deep inspection doesn't find damage