I don't own any Choos that are that high, so I'm not sure. I will say I've been pretty lucky with my actual shoe size with Choo boots and flats and lower heels though. Have them do a measurement of the footbed for you and then measure a pair of your shoe that fit. Those are very nice shoes!
I have 4 pairs of Choos...all are flats. 3 are 38.5, and the 4th is a 39. I usually wear an 8.5 to 9, but find the Choos fit me better in a 38.5. I cannot wear heels (post knee surgery), but when I did, I seemed to wear 9s most of the time. My foot is average width.
I too have found the shoes to be all over the board
Black Prince Boots: 5.5
Also, a pair of flat loafers are 6's, but I tried 3 sizes in the Wilton flats and 6.5 was too small and a couple of other pumps were 5's
I wish they were a little more consistent with their sizing since they don't have boutiques all over the US to allow you to try on various stylesush: