i have done 14lbs @ 60.2%
10 lbs yields me high 70's
make a 4 gallon batch, use 14lbs, and boil for 2 hours before you first hop addition
nah, seriously tho, to make a 1084 beer, i used 15lbs of grain, and split it into 2 mashes/4 sparges... ended up 9 gallons in the kettle, and started the boil with the first runnings!
long ass brew day.
im tellin everyone this....home depot has a 10 gallon round rubbermaid you can swap all your 5 gallon manifolding into for about 40 bucks out the door. then you could easily do 22lbs of grain! IIIPA !