I allow it
My number follows Gregory Urich's whitepaper "
Analysis of the Mass and Potential Energy of World Trade Center Tower 1"
Urich very carefully lists as many building parts as he can, and tallies a total mass of 288,100 metric tons, versus your 455,400 metric tons. That is the first source of difference.
Where did you get your mass per floor?
A second source for difference is your assumption that all floors have the same mass. That is pretty much true for the floor assemblies and office contents; Technical floors would need special attention.
However, the steel columns are much heavier in the lower floors than in the higher floors, so mass per floor decreases from bottom to top.
Urich determines a total potential energy of 480,6GJ vs. your 942GJ. This would mean that Urich's center of mass is at 170m, or 41% of the height of the tower, rather than at 50% (207m).
I chose Urich because he is at the same time meticolous, transparent and conservative. It doesn't hurt my arguments if I err on the low side.
As a side effect, that mass estimate means that the twin towers had an average density of 0.17g/cm
3. I once looked up that this is about the density of large ships, so I am probably not overestimating; ships need to withstand forces from a greater variety of directions.
Assuming that this density, and the relative height of the center of mass, applies to other steel frame highrises, I estimated the potential energy of the WTC7 to be 80GJ.
Here two blog posts I wrote to myself about this:
WTC1
WTC7