To add my 2cents....60lb bow is plenty to shoot a deer out to 40yds no problem. Shot placement is key. a 60lb bow will shoot straight through a deer just as easy as a 70lb only difference is how far in the dirt its stuck...again just because its a 70lb bow doesnt make it kill any quicker/better...
Also if you have shoulder problems 70-80lb bow will surely mess it up even more. I have some shoulder problems and the 60lb is doing just fine for me.