Re: Hook Eyes Up/Down/Straight?
Originally, wire hooks did not have formed eyes. They were made by hand & I guess the means to form such a small eye didn't exist. The attachment to a line had to be done via a lashed connection prior to dressing the fly.
I'm not certain, but expect that later as better tippet materials were used, snelled connections may have been used & that resulted in the up or down eye positions. Hooks still have either IMO more so due to traditions rather than actual function.
I don't use dry flies very often, it's been many years since I've even tied one, but I've always used dry fly hooks with the down eye. I rarely tied smaller than an 18 even when tying commercially, so had no need to up eye dry fly hooks. That up eye on such tiny hooks may expose & open up the hook gap a bit more than a down eye.
Agree that a Turle Knot is fine for either up or down eye, but which came first, the knot or the eye positions? I can't answer that!
For nymphs, streamers or anything else I like straight eye hooks, primarily because I use a loop connection most of the time, but have not had any issues using down eye hooks with loops.