I've been vegetarian(ish - I eat meat approximately once a month) for 5 years now, and recently discovered some amazingly good fake chicken. Which prompted a discussion with my dad about the efficiency of fake meat products. We hear a lot about how cows give you only 1 calorie per 40 you spend producing them (or maybe it's 1 per 13, I remember both figures and there was a difference between them, but I can't remember what).
Chicken was better, efficiency-wise, but still not as good as actual vegetables. But I haven't heard anything about the energy efficiency of fake meat products (made from soy or something similar). They're usually more expensive, but we figure that's more of a supply-demand thing than an indicator of their energy efficiency.
Google-fu gives me some interesting stories about ,"real" meat grown in vitrowhich I totally support. But which aren't relevant yet.