Size really isn't all that important in pork butts as most commodity pork is between 7-10lb range. It's the money muscle that makes all the difference. I try to find two that are similar in size. We have found that 16-18lb's on the brisket works best for us. Would like to find bigger but it's easier to find good marbled prime briskets in the 16-18lb range out here. typically on the larger ones there are few to pick from so your stuck with buying the one they have. We like to pick through for what we think is the best for us.