I think it's a matter of personal taste, but I would generally go with the topmost, except to keep the normal Z.

Thanks cerulean

For the /K/, I'd try something based on the I< (look at Meta for example), style construction to minimize the dark spot (if that makes sense).

JamesT, that that makes sense :) Will try that as well, how about the over all font ? I know it's raw yet but ... any thoughts?

Too tall.

I wonder if the median horizontal bar of /K/ and /X/ crossing should more closely match /B/E/F/ (I assume you chose the upper variant, excepted /Z/).
I don't know if it's too tall, but certainly I see /f/ and /t/ suffering.
/i/ and /j/ shouldn't have same x-height?
an finally, I'm not into /x/ form.
But in general I truly like the font face :) let's see figures!