I've got one of the Barney external frames and have used it for sheep, moose, caribou, etc... over the past 6 or 7 years. It hasn't let me down, yet.
Having said that, I'm considering trying a good internal frame pack for this years sheep hunt. I really like internal frames because they are less cumbersome and hold the weight better. Meat will have to be boned-out, and put in trash bags, I think to make it work though. Sometimes in the iffy areas, the external frame can get in the way. I've got an internal frame for work and camping that will hold more than I can carry, so I think it'll work as far as weight and mass goes.
What do you guys, think?