From our calculations, the only thing wrong with the above is that our 550-600 kg cows eat 1.5 - 2% LW in DM/ day…Assuming average daily requirement of 3% LW in DM per day the 800kg herd will eat 2,400kg DM per day.
The 550kg herd will eat 1,650kg DM per day.
To be a proper comparison it should be 100x 800kg cows Vs 145 550kg cows.
Assuming each herd weans 95% at 45% of LW, it's 95x 360kg calves Vs 137x 247kg calves.
I'd take the more numerous lighter calves. More head to spread fixed costs over, and each death is a smaller percentage of total income. But that's because I'm a clown and sh!t stockman.