A character can lift up to double his maximum load off the ground, but receives no bonus to AC from Dexterity and can only move 5 ft. per round as a full round action. The rules seem to be silent, however, on what check penalty such a character would accrue. Presumably a character staggering under such a load could still attempt an Acrobatics check to stay balanced, or a Climb check to escape a pit - at an appreciable penalty. But what would that be? I'll go with -12, unless there is an official answer to this question.
A character can lift as much as double his maximum load off the ground, but he or she can only stagger around with it. While overloaded in this way, the character loses any Dexterity bonus to AC and can move only 5 feet per round (as a full-round action).
I would use the Heavy Load penalties combined with the changes to the penalties during lifting an object. So the penalties are:
Max Dex: No Dex on ACCheck Penalty: -6
Speed: 5 feet as a full-round action
Escaping a pit sounds ridiculous with a 5 feet step :)