So we're having a bit of an argument about a character swinging around a sword that's the size of a small building, but that's besides the point.
The question at hand is: Does Enlarge Person octuple the weight of gear, or double?
So the two conflicting points is what part of the rules should be followed in this scenario. The rules for large gear for larger creatures goes as follows:
Weight: This column gives the weight of a Medium version of the weapon. Halve this number for Small weapons and double it for Large weapons.
The rules for Enlarge Person goes as follows:
This spell causes instant growth of a humanoid creature, doubling its height and multiplying its weight by 8.
All equipment worn or carried by a creature is similarly enlarged by the spell.