Again we can't compare them as we have no idea of the input energy to each rifle compared to the output energy, Barry.
So no direct comparison can be made, it could be that the 460 is acheiving the same power with a reduced input energy.
If you research airflow in pipes, you'll find there are calculations for the energy loss caused by air going round bends compared with moving in a straight column.
Strange that Diana should go for an offset transfer port on the 460 Magnum if they truly believed a central transfer port has a major power advantage.
BTW, I wouldn't be able to choose between a 77 or a TX given the choice, which is why I own both.
All the best Mick