In addition to the previous two valuable comments, I will give my .02 in this regard. From my own experience with 3 real projects so far, I can tell that, no matter the measurements with formulas or software simulations, the only way to properly consider the compress strength of a door gas strut is to test it in the real life, complete with the power window, latch, inner door skin, hand rest and basically everything installed. Sometimes, even couple of kilograms or pounds may lead to improper- or not good enough operation of the gas strut.