Area - area - area. Like dun says, you have to match your resources & market to the size of cows.
In our area, the extension even preaches that we need larger cows out here. Now, larger, meaning BIG VOLUME heavier weight cows - not 9 frame 1600# - more like 6 frame 1400-1600#. Also, remember when you're talking maintenance - it's not just how much she eats. Its every cow, needs to be worked thru the chute for vaccinations, every cow needs to be calved out, every cow needs MANAGEMENT. I would rather take care of 40 GREAT cows than 60 mediocre ones. This holds true even for a commercial herd.