Coincidences are amazing things. Thirty years ago, when I made my first trip to England, I bought, in the gift shop on board the Cutty Sark, a most interesting booklet: a reprint of an article from the 1966 Quarterly Transactions of the Royal Institution of Naval Architects. The article was entitled "The Restoration of the Cutty Sark," by Frank G.G. Carr. He was in charge of the actual restoration process, in the late fifties and early sixties. I remember reading it voraciously that evening in the (incredibly cheap) London rooming house where I was staying, and I kept it for quite a few years until it disappeared after a move. Recently I found a copy of the same, reprinted booklet at a used book site called www.bookfinder.com, and ordered it. It arrived the day before yesterday. I spent some time last night reading it again. Lo and behold, it contains a reference to the Yachting World article davidson3 has been looking for.
Here's the relevant quote (from p. 214 of the Carr article);
"I have...discovered, since my paper was presened, that in the Yachting Monthly for February 1930, Vo. XLVIII, No. 288, pp. 291-293, there is a valuable comparison between the lines plans and sail plans of the Thermopylae and the Cutty Sark, in an article by Mr. Leslie Knopp, M.Sc., Ph.D., who was a member of the Institution until the end of 1957. Mr. Knopp had made tracings from the authentic original, which he told me he had borrowed for the purpose from the late Mr. Arthur Briscoe, the well-known marine artist. I therefore got in touch with Mr. Briscoe's son, but learned that unfortunately there was no record of these plans among his father's papers, and certainly they were not found after his death....
"In his comment on them Mr. Leslie Knopp wrote: -'Thermopylae was the first well-known departure from the high rig as compared with width of canvas. She never had skysails and moonsails like her contemporaries, but her royals were the largest ever set, being about 19ft. deep on the main! All her masts were shorter than Cutty Sark's, and her yards were longer. The lower rigs told in a quartering breeze and Thermopylae could run at over 13 knots with every stitch of canvas set, and it was not until 14 knots had been passed before the royals had to be taken in.'"
Mr. Carr also reproduces the lines plans and sail plans of both ships. They're quite small (the hull lines about 5 1/2" long, the sail plans about 3 1/4") and without much detail - but there's enough there to make it obvious that, contrary to what Revell would like us to believe, the two ships were quite noticeably different from each other.
I'm afraid that doesn't add much to what davidson3 already had - though it does nail down the date of the Knopp article and establish that it was only three pages long.