I'm not sure thats right Wez, I was just trying to do some calculations and It doesn't seem to work out . . . IIRC the gravity remains constant, so between 70-75 gravity points of course the amount of sweet wort you run off increases which means that you dilute less to get higher gravity beers. I am sure that you can appreciate that this becomes seriously inefficent as your desired OG goes up (IIRC I used 29Kg of grain to do 5 gallons of a 1.102 Barley wine a few years ago

Of course I ran off 10Gallons of 1.050 Table beer from the spent grains as well

)