@haskafah – A great discussion indeed. Thank you for ypur participation and contributions. I don’t think there is any machlokes as to what defines halachik peyos (see the Mishnah and Gemora in the third perek in Makos, theRambam, Shulchan Aruch, etc.). Two reasons have been brought in a number of sources for the basis for longer peyos. One is found in either the Sefer HaChinuch or the Minchas Chinuch; to make it clear we do not do as the non-Jewish world (e.g. monks) who round their corners and we therefore specifically grow them longer. Another reason, brought inbthe the sefer Maamar Mordechai, I believe, is Zeh Keili v’anveihu.
On the subject of short jackets which you mention, the famous teshuvah from the Noda BiYehuda says that the first Yid to go short was “following the chukos akum, but ince he did, there us no Torah issue of not going long. But, once again, that IS the way all Yidden went until, for various reasons, a change was made. But once again we see a RE newal and a REturn to the original order.