Since this thread came up again and needs pics, here are the largest and smallest frames that I ride regularly.

https://cimg3.ibsrv.net/gimg/bikefor...8ee814a9d.jpeg
The AustroDaimlers are 62.5X59 ctc
https://cimg2.ibsrv.net/gimg/bikefor...f423dac221.jpg
The Bottecchia is 58X57

This bike has a bit more than a fistful of seatpost showing but, as a taller rider, I was excited to find this 64x62 cm frame.
https://cimg3.ibsrv.net/gimg/bikefor...7839e8b794.jpg
This has even more seatpost showing (and a shorter headtube than I'd like - shorter top tube sort of makes up for the less reach, but it's not as comfortable on my back as the above), but again, beggars can't be choosers. I was tired of being without a bike after my previous one had been hit and the above was still in the frameset state and the BB was both bad and seized to the shell, so it wasn't usable. This 62x59 cm frameset was what I could find at the time.
https://cimg3.ibsrv.net/gimg/bikefor...bb27757591.jpg

Given a little saddle clamp setback and room on stem for bell, it looks nicely balanced. Not a bad find, if I may say so.
https://cimg1.ibsrv.net/gimg/bikefor...559b7d963c.jpg
Nice simple photo, too

Your Bottecchia is just plain sweet. Are those the old Universal center-pull brakes?

A hot topic for sure and I guess the industry would say you need to get a professional bike sizing to get the best fit, or at least that's what I keep seeing in videos. I think it makes sense to get a bike sizing but what about having multiple bikes, never mind multiple bike types? I have a newer Cannondale bike, 56 cm that I feel fits me quite well and I can ride it for long distances with minimal issues, despite never having got a bike sizing. But then I jump on one of my older steel bikes and now I'm on a different bike geometry and so does that impact the comfort I should have?

Same thing when I ride my 90's mountain bike which is a different geometry and different sizing consideration than the road bikes.

Yes.
The original owner only changed 1 item from factory build - the rims from tubular to clincher. I swapped the Record RD to NR, a better seatpost/clamp, and use a tubular wheelset. New gum rubber hoods. Very nice ride. Columbus SP for tubeset (I think), which is good for my 190lb body.
https://cimg0.ibsrv.net/gimg/bikefor...8a7875b14e.jpg

I went into two dealers this week, both are telling me about a year for a frame. When my eyes bulged, the guy said he has a customer who had been waiting 3 years. That is one reason someone might be on too small of a frame.

I used to be 6'4'' but measured recently I am only 6'3'' with 36' inseam (crotch bone to floor) with a 1.04 Ape Index. I'm riding a 58 cm frame with a 396mm reach and 605mm stack, 73 degree seat tube angle, 25mm setback seatpost and a 150 mm stem. It fits on paper or video for the fancy expensive fitter. I got sold that frame size by a shop with a good fitter but it never felt right.

Does it fit on the road? Not really. I dominate the thing. Balance isn't right. Too small. As an example, I have a steep bumpy descent with some corners. It is a handful for many reasons. I recently took out another bike on the same hill, it is more of an endurance frame than a road racing frame. Going down that hill, I thought......man, is this bike slow. I looked down and the Garmin was saying the same 40 mph as would be about the case on the "racing" bike. It was boring. It might be a little big but I only need a 120mm stem on it and the longer wheelbase and trail seem better to me than too long of a stem with my ass hanging off the rear wheel trying to keep it straight on steep bumpy descents. I might be wrong here.

That Bottecchia has the perfect early '70s vibe. It reminds me of Doug Dale's venerable Cinelli Corsa A.

Universal made very nice brakes. When I built up my Roberts with #68 sidepulls I took some grief from my friends, but they served me very well. Do you have photos of the Follis and Zeus? Many many years ago I connected a girlfriend to a beautiful Follis 972 that was practically made for her. And I always regretted impatiently jumping on a Raleigh International instead of waiting for my flaky neighborhood dealer to find me a Zeus.

I ride a lot of different road bikes with a 5cm range in frame sizes (58-63cm in traditional, level tt sizes) very comfortably. For me the 'perfect bike fit' has a lot of range, given all the variables. Lucky to still have decent flexibility. And a desire to ride them all. Admittedly, the 58cm ones would not be my preference for a leisurely century. As the 62cm+ would not be my best climbing bikes.

With the latest bike purchase, I was advised by online calculators and a LBS to get a size large. But this one may see some gravel, so I wanted the longer wheelbase and I do like to stretch the upper body, so I sized to XL which closely matches my other carbon fiber bike. Maybe my arms are long for 6'1".

To me life is too short to waste time riding a poorly fitting bike. If I had to wait for my halo frame, I'd probably get a "transitional bike," something like an Allez or Emonda ALR, just to be riding something that fit properly.

The last time I was in the Whitefish, Montana, area, I rented an alloy BMC. The shop gladly set it up just right for me, flipped and slammed the stem, and after a couple of days riding it, I had to say I wouldn't mind if this was the last bike I ever owned. Because it fit properly.

https://cimg0.ibsrv.net/gimg/bikefor...a5622b39d8.jpg
https://cimg0.ibsrv.net/gimg/bikefor...00ea1d3e7c.jpg
https://cimg4.ibsrv.net/gimg/bikefor...8cf8491947.jpg
The Follis is either 072 or 172. Falck tubing. The bottom model available. Put a 46/30 crank and cyclocross tires on it and it was my offroad for a while. Now only a frameset.

Simple answer, from personal experience, much rather have 1 size too large.
Tim

Wildwood, I'm in love with your Zeus. Is it, by chance, a 60 cm?

I get bikes by the effective top tube length, not the manufacturer's size or seat tube length. That makes a lot more sense and makes the choice of frame size simple - you immediately see what your stem length might be.