I usually boil about 2 - 2 1/2 gallons and make up the difference at the end for a 5 gallon batch. But I have been letting the wort cool all the way first, then adding water to my primary, along with the cooled wort. So I was thinking at flameout why couldn't I just top my kettle off with as much cold water as I can, along with letting it sit in the sink with ice water.