That is an ambigous question. Beefmasters run the same size as other beef breeds. You can find them small, 1000 lbs up to 14 or 1500 lbs. The ideal size in my openion is about 1200 lbs.
As in other breeds one can expect to get about 60 to 65% of live weight meat from a bovine. A 1200 lb. steer should yeald about 756 lbs of carcus on the rail which is the pay point. Cutout during the processing will reduce the amount of available meat even more. It is true that the more waste, fat, flab and loose skin will reduce the yeald. It is because of the waste that the Brahman influenced breeds have cleaned up their cattle (reduced the size of the loose skin in the brisket area for example) to reduce the amount of waste.