I've shot Hornady 68 grain BTHP in a 600yd stage with my 1:9"... It was my first time out of the reduced-range leagues. The only comment that I can make is that they all hit the paper...In one case, that of my neighbor. ;-)
The Hornady 75gr was designed for the 1/9 twist barrels, but they do not work well in all of them. The reason is that not all are truly 1/9, some are closer to a 1/8.5, and some are closer to a 1/9.5, and then how tight they are. You just have to try them and see if your barrel will. Otherwise, go down to the 69gr BTHP and shoot away. You won't get as good of a score in the long run, but if you are starting out, they will probably out shoot you.
The 62gr SS109/M855 bullets are the length of a 69gr bullet, but are lighter due to the steel penetrator core. It is not the weight, but the bearing surface length that matters.
If you already good, or when you get there, put on a 1/8 or 1/7 twist barrel and move up to the 77 or 80gr VLD (not magazine length).
The bad part is that if you are using anything lower than 75 you are going to be at a pretty big disadvantage because I think the hot bullets (because they freekin work) are the 77 and 80 smk's and those darn new 80 amax's. Those are the top three I see now a days. I shoot 80 smk's with a 1:8 stainless barrel.