I would think that arrow length would be fairly fixed based on your draw length. So that leaves arrow mass and arrow speed (based on draw weight). You will max out draw weight at some point either through physical strength or the bow's specs. If I have to choose between arrow mass and speed it will be arrow mass every time.
Another thing to consider is that even though you may be able to draw 60 or 65 or 70 pounds in shorts and a tee shirt standing flat footed in the yard practicing this summer, it may be a whole different story this fall when you have been in a tree for 4 hours in 30 degrees and you are presented with a weird shot angle. For example, I can draw 70 pounds if in my backyard but I hunt with 60 and 44 pound draw weight bows. I can draw that 44 pound compound from just about any position I want, and it was plenty to break a buck down last fall with a 585 grain arrow with 23% FOC and a single bevel broadhead. It is also dead quiet with that somewhat heavy arrow.
Another thing to consider is that even though you may be able to draw 60 or 65 or 70 pounds in shorts and a tee shirt standing flat footed in the yard practicing this summer, it may be a whole different story this fall when you have been in a tree for 4 hours in 30 degrees and you are presented with a weird shot angle. For example, I can draw 70 pounds if in my backyard but I hunt with 60 and 44 pound draw weight bows. I can draw that 44 pound compound from just about any position I want, and it was plenty to break a buck down last fall with a 585 grain arrow with 23% FOC and a single bevel broadhead. It is also dead quiet with that somewhat heavy arrow.