I have a 9 gallon pot and have done 15.5 lbs for a 1.077 beer. Wasn't easy but I did do a mini sparge with about half the grains. My biggest problem is pulling the bag out.......gotta use a collander and remove a little at a time into another bag. Luckily, most of the beers I brew (IPA) are 13 or under and work out very well.
I have a Barley Crusher and set on factory default, it crushes awesome. I average about 80% efficiency with no sparging but I do let me grains drip for a long while as the boil gets going and that seems to work well.