What would it take to make beef production more efficient? genetic engineering perhaps.
People wil naturally switch to more efficient food as population goes up and food resources become more scarce.
So I think the answer to your question about increasing efficiency is probably pretty difficult. There's already a huge profit motive to increase efficiency, so if a few labcoats could easily solve the problem I'm sure they would have by now. I think the answer is to eat animals who reach maturity faster (or just grow more per unit time?). Like insects :-)
Nothing. Large animals that live long lives are inefficient by their very nature. The bigger an animal is, the more of its energy consumption goes to maintenance rather than growth. And the longer it lives before reaching slaughter weight, the more that inefficiency compounds. If you somehow turned cattle into 5 pound animals that mature in 6 weeks, they would be efficient, but they also wouldn't really qualify as cattle any more and their meat would likely be noticeably different than beef.