I did stop when the runnings were down to 1006 - I had about 1-1.5L left in the bucket when I stopped - maybe the last sparge could have used less water, so I could have used more of it.
Well I managed to get 5 bottles out of this in the end! Hopefully I'll get a better yield next time, but for now it tastes fantastic. I get the distinct feeling that my kit days are numbered...