Id go with the 60-70, just because it allows you to increase if you ever want to. 50-60, you are limiting yourself. If you are already shooting in the 60lb range, it would make no sence getting a bow that does not meet that range. Peak weight is more efficent, but then agian I dont think enought to make a difference. If you spend the money for a bow, you would kick yourself if you felt like increasing down the road. I like shooting 70lbs with a 65% let off. I did not get there over night. I started at 55lbs about 20 years ago. More I shot, the stronger I got. I upped my weight to increase my KE and to get less drop.

that is my oppinion. Id do what feels best for you.