I am okay with the basic fit now (thanks to the kind advice received and will purchase a 140mm stem from China) but I think that angle of the stem and the height of my bars will be a personal thing (how supple I am, how much I am prepared to go down low to achieve aerodynamic form).

So I want to try various different angles. I can't use that shim (unless I can find another stem it it fits). I did look into a variable angle stem but I am not seeing them in 140mm in my price range. Another way is to vary the spacers. I have already moved two of them above the bars (strange how I can't get rid of them completely), and I am wondering what to do about the cone shaped spacer, which if removed would be another way of achieving lower handlebars.

Or does angle as opposed to height make a difference?

By the way I would still be very interested to hear of the disadvantages of having my saddle so high and my legs extended at the full thrust of my pedals.