I am making more of Denny's Imperial Porter so I can fill up a 15 gallon whiskey barrel. It's really remarkable how much difference I can have in two brew sessions. Last week I got almost 75% efficiency on a 1.086 beer and this week I have had to boil for an extra hour to increase the gravity to match.
You'd think I would know how to do this after 25 years, but no.
Edit to remark: Woo Hoo! Post #3000!