I still don't see why they can't haul the chart straight out of 3.5:

At 10 str (average) a character carries 33lbs unencumbered, up to 100lbs encumbered. Can lift 200, push 500.

At 18 str (normal max) a character carries 100lbs unencumbered, up to 300 encumbered. Can lift 600, push 1500.


Seems much more reasonable to me.