Thank you both.

It's unlikely that I'll split these into two typefaces as there are too many letters I'm not very happy with - the E and F being two prime examples. And because of their construction, there's no way that I can think of to reduce their width by a sufficiently subtle amount. Their current shapes are a sacrifice of letter-width in favour of line-width, as the image below should hopefully illustrate.

The thinner K construction should give an idea as to how awkward some of the shapes were to build - deceptively difficult in places. And the bold S is one letter that will never maintain the smoothness of the other forms.