Yes, about 70-85% efficiency is all pretty normal, and anywhere in that range would be what I would consider to be a good balance between flavor and not wasting too much money. If your efficiency is in the 50s or 60s... that kind of sucks as you're wasting money, but on the other hand, you'll make awesomely malty beer that way. "They" say that the lower your efficiency, the more malty the beer can be. For instance, if you do a no-sparge beer, you might only get 55% efficiency, but dang that beer tastes nice and malty because you're essentially making the beer out of nothing but first runnings. You're not watering down with a lot of sparge/rinse water that needs a long boil to be concentrated. Nope. Just first runnings. So yeah, efficiency sucks, but yum.... So that's kind of where I got my theory from for the other way around. I can achieve 95% efficiency, but this requires a really hard crush and a lot of sparging. So, you're getting more sugar out of less grain. So, since you're using less grain, you get less grainy flavors. That's the theory. To date and to my knowledge, no one has bothered to prove it right or wrong. I need to run more experiments. Eventually. Maybe.
Thanks for the thoughtful answer!