amount of meat in here?

ok if i went with this grill just how much meat could i fit in here?
my local sams club has the boston (i think lol) pork butts at about 2 10 # butts in a package and 8 in a case
they are about 10-12# average
how many could i fit on this grill.......says 626 sq inches cooking space so im figuring its about 20 deep and 30 long
http://www.pelletgriller.com/product/id-5

so 4 big or 6 small?
if i was going to need to do 8 what sized grill would i need?
would an 800 sq inch be enough?