that's not entirely correct heuhen, an spread out weight requires less strengthening then 2 shorter heavyweights.
Yes you are correct on that, but you need also extra strengthening for the bigger opening.
Bigger the opening is thus more strengthening beam needs. (for example: her in Norway we have two bridges next to each other. one of the bridge is about 20-30 meter long than the other bridge (around 10-15% longer), but the steal needed, compared to the smaller bridge was around 20-25%. (you see it's not always something is proportionate the same)
for the 2 for 3 ratio on the GMLS. was just something a took out of the lose air.
But if we know the weight of the tree standard GMLS and put them in an graph. the we should be able to give an approx number on how heavy it can be.
But hey we are both right on some, isn't that better that "one" is right on something