This morning I found something that may help us determine -- with a fair degree of certainty -- the origin of David Ogilvy's most famous headline.
The book, Advertising in America: The First 200 Years, has hundreds of old ads -- including the Ogilvy & Mather Rolls-Royce ad, which they reproduced on nearly a full page. (Readable copies of this long-copy ad are available in some books, but they're hard to come by on the Internet.)
The opening paragraph of body copy may be our smoking gun. It reads, "'At 60 miles an hour the loudest noise comes from the electric clock,' reports the Technical Editor of THE MOTOR."
It looks like David Ogilvy or one of his colleagues simply pulled the Rolls-Royce ad headline from a line that appeared in a printed MOTOR article -- a perfectly reasonable and legitimate thing to do. (Notice the quote marks around the headline.)
This means the Technical Editor of THE MOTOR may have deliberately worked off the oddly similar Pierce-Arrow headline, but that's beside the point. Basically, if we see the "At 60 miles an hour..." sentence in a MOTOR article from that era, we'll have what may be the closest thing we'll ever get to a definitive answer. (Yes, a cynic might say an O&M employee could have fed the Technical Editor that line, with full knowledge of the Pierce-Arrow headline, but I don't even want to go there.)
Unfortunately, THE MOTOR -- which was published in the UK -- isn't listed in the Reader's Guide to Periodical Literature, and copies from that era are rare. But I'll try to find someone able and willing to go through relevant issues. Stay tuned.
P.S. For your convenience, here are each of the two 18-word headlines:
The only sound one can hear in the new Pierce-Arrows is the ticking of the electric clock.
At 60 miles an hour the loudest noise in this new Rolls-Royce comes from the electric clock.