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.
Remember, no one likes to be behind the big truck, but that's better than being under it!