HSWL
Back in 1954 I was working on parachute flight testing at RAE. Then the opening load depended on what we would all think (size and speed at deployment) BUT there was another factor that was very important and that was the porosity of the fabric. The porosity of any fabric can be shown to reduce with altitude. This means that unless a parachute is designed to be used at high altitude then it will very likely split (or otherwise fail) if opened way above its design ceiling. There is also the IAS/TAS issue which will certainly affect the opening shock loads and again at 40k the TAS is twice the IAS so any forces related to inertia will be doubled.
JF