I'd say most afghanis are well under 200lbs.
The weight limit is likely more a pressure and CoG loading thing than anything else - the entire floor covered with people experiences a lower pressure than the load distributed through the abrahms tracks but the CofG may stay the same as with the tank or may shift around a little.
In terms of overloading, you just need to fly a little bit faster (to double lift you only have to fly 1.4 times faster everything else being equal)