I don't have any Carminas but, time ago, a member sold a gorgeous black balmoral on Simpson last. Pristine! UK 8.5. The length was 11.89" -I remember it very well because it seemed quite short to me. So if you add 0.4cm -which is the normal increment for each half size- you get 30.6 cm. Having said that, I also read some posts pointing that Simpson's UK 8 length is almost equal to Rain's 7.5 UK -which called my attention given that Simpson's insole length is a tad longer. A 9 UK equal or shorter than 30.5 cm looks short to me -unless the last is longer that the sole which it's perfectly possible.
Sorry mate, I think I have not been very helpful. I have probably increased your doubts.
Anyway, as most of the member mention, you should focus on the insole dimensions rather than the outsole if you want to find your best size.
Thanks @Ugrant
Any information is welcome.
And yes, it's a little bit surprising what you say about Simpson's length (half size down) being almost equal to Rain's one.
If we look at the insole measurements provided by Peitron we clearly see Simpson is 1 mm longer. Interesting.
Perhaps those posts you mentioned we're based on just a visual comparison (not measured with a tape)
Let's see if someone could throw here some measurements.