The specs of the standard speedy are misleading at 42mm, automatically projecting larger size watches from other brands. I can confirm that a 42mm Moon Watch fits better than a +38mm ‘57 Trilogy both of which I’ve had. ...
How about the fact that 41 mm Bulgari Octo Roma has 45.6 mm lug to lug, while Rolex oyster perpetual 39 mm has 47 mm lug to lug. Even surprising is most of the Longines watches has very long lug to lug , for watches with 38-40 mm diameter.
wears a lot smaller than the numbers suggest. I have quite slender wrists at 6.5 inches but the Speedmaster Professional sits better on my wrist than a 114060 Submariner despite being 2mm larger on paper. I guess the asymetrical case and twisted lugs are ...