oldbobcat

Axel Merckx, Eddy's son, has a similar build--all arms and legs. Eddy and I lean in that direction, but not as bad. I'm 5-11.5 with 35" legs and a 75" wingspan. In modern bikes, I've found 57-58 cm fits well if the top tube doesn't go over 57 cm. I have a '80 Masi, 60 cm with a 57 cm top tube, that fits me perfectly. With the seat clamp reversed it looks like your upper body position is quite vertical and your leg extension is a little short. I'd venture to say you could get more leg extension by moving the saddle back. You might also get more power and better handling with a lower back angle and lowering the stem. Start with the shorter stem, then see if you can use the longer one without crabbing to the front of the saddle as you ride.

One advantage of those old British frames for you is the top tubes on the taller sizes tended to be shorter.

tangerineowl

Came across this frameset for sale today:- https://groups.google.com/g/650b/c/xmkkpO7dQrA

Raleigh Gran Tour steel 531c with 531fork, at seat tube 64cm ctt, with toptube 57cm ctc.
73/73 built by Raleigh Special Lightweights div. 700x35 or so.

oldbobcat

Case in point, a tall British frame with a short top tube. The proportions for the International are more conventional.

tangerineowl

Naughty thread bump.
Here's another UK frameset. 531c.
63.5cm / 57cm with a 21cm headtube.
https://www.lfgss.com/conversations/388416/

Finding these type of frame proportions is a bit of a hobby of mine.

tallbikeman

When going to a smaller frame be aware of your knees hitting the handlebars. Smaller frames by design will bring the handlebars closer to your knees. Your Felt and Trek did what they are supposed to do. They make you stay in very aerodynamic positions which is your upper body almost parallel with the ground. The seatposts are not out too far from what I see being ridden by the high performance crowd here in Sacramento CA. If you are migrating away from these low handlebar positions then coming to terms with that will answer a lot of questions about sizing. If you like your present handlebar setup which is much higher that your previous bikes then so be it. Any new bikes should be able to reflect that handlebar position just as you have it on the Dawes. I really like your old Dawes. Even though it is not top of the line it is still a fast reliable bicycle and you will surprise lots of people who think somehow its the carbon and not the legs.

Kontact 

I've looked at an awful lot of old geo charts, and I have yet to find a common production road bike with the legendary "criterium geometry" compared to today.