For what it's worth... :

My 1976(?) Holdsworth "531 Special" 650b conversion ("Gugificazione") and my 2016 Square Built custom have the same geometry and dimensions: both have 60 cm (c-c) seat tube and 57 cm top tube, very similar fork offset (hard to measure, around 6 cm). Both have 73° parallel head and seat tube with horizontal top tube. They have different wheels, but a similar wheel diameter.

That is, the Holdsworth takes 584x38c tires (so nominal diameter 660 mm) while the Square Built has 559x53 tires (so, nominally, 664 mm). I emphasize the word "nominal" because at present the Holdsworth has a 42 mm tire in front. Which would make up the difference. But as I measure them the difference between the 38 and the 42 is really negligible, definitely less than 4 mm, so let's continue to emphasize the word "nominal."

Obviously there is a significant difference in the width of the tire, but that is really the only significant difference that shows up in the numbers.

The Holdsworth is butted 531, the Square Built is Columbus SL; the frames weigh in around 74-76 oz, I don't have the numbers on front of of me. If I recall correctly, the SquareBuilt has an appreciably heavier fork.

Anyway. You're wondering: what's the point? Well, the bikes handle differently. The Holdsworth has a tendency to shimmy, the Square Built does not. The Holdsworth feels more responsive, more agile. Both are comfortable, but the Square Built moreso. Neither is appreciably faster (they have the same engine). But they really feel like different bikes. They [iI]are[/I] different bikes.