Afaik, the internal weight of cargo in the Chinnok can be up to 10,00lbs, and the external can be up to 26,00lbs. Might want to google it though.
As for choppers in game that can actually do this, take a look at Afrographx's chinook
http://ofp.gamepark.cz/index.php?showthis=9976Also BAS's one, as you've already mentioned. These can have vehciles inside, but can be scripted to have a underslung load.
As for the hummers in a C130, it could be done with scripting, but i'm not sure how exactly. You wouldn't be able to see the hummer in the plane though. Ask in the editors depot and see if anyone knows how.