I would like to know also.
I have shot a bow with 50% and one with 65%. The one with 65% I shoot alot better so that is why I ordered my XT with 80%. I thought maybe I would give it a try if I do not like it I can have it changed to 65% and yes I know I will lose 1/2" on my DL. So I guess this is something more of personal preference also, just like different bows. I hope someone can help you out here with this question. Later dude.