I'm currently getting 55% to 65%, I feel like this is low... what is expected from Single Infusions?
I get 75%-80% on my infusions. Personally, I think the biggest factor in efficiency is how your grain is crushed, and how fine of a crush your lauter tun can handle.
I get about 85% according to promash. It used to be about 75% before I did a mash out, and adjusted the sparge water temperature so that the sparge was conducted at approx. 168. (I fly sparge.)
I'm at about 55-65%. My malt is inexpensive, so I just throw more malt at it. I get about 2.07 lbs malt per degree of plato currently.
Mine jumps between 65 and 75. Making sure your sparge water is at the right temp and sparging slowly can make a difference. Most people here have said that a finer crush makes a big difference. You could also try a longer mash.