I prefer the 42 mm version.
To say all, I think the 40, 5 mm is a mistake.
The two dimensions give the impression, the feeling that JLC is " waving " between the two case sizes while they only wanted to offer a smaller versons for those who prefer smaller watches.
I would have a different opinion if JLC had released the 40, 5 mm for a new Duometre, I am not comfortable with the same model coming in two different sizes.
Best,
Nicolas