Originally Posted by jackal

IIRC, this was asked somewhere on FT previously, perhaps in the United Airlines Pilot Q&A Thread. I know FT's search function doesn't always work well, but if you search all forums for "planes slower save fuel" or something like that with display by posts (not threads) selected, you might come across something, or try Googling "site:flyertalk.com planes slower save fuel."

Of course, if you don't come up with anything, I could be misremembering that it was ever asked in the first place...