These forums have taught me alot. One ofthe biggest facts that I have learned from forums and proshops is that you gain no speed ,or very little with a 70# setup over a 60# setup, due to the heavier arrow weight required from the heavier spined arrow. If you keep the recommended grains per inch per pound, both bows will shoot the same in speed. You only gain more kinetic energy from the 70# arrow but with a 60# setup you are still over 15 ft pounds of the recommended kinetic energy needed for bear, elk, or caribou and over 25 ft pounds of the recommended kinetic energy for a whitetail deer. A 60# bow will kill anything that walks the North American continent. Considering that 90% of all bowhunters will never shoot anything larger than a whitetail deer, these heavy poundage bows are just not necessary. Years ago when bows were not efficient at delivering and producing energy, maybe 70# was a great merit in a bow; but not with these new modern bows. My newest bow, a 29" Guardian peaked at 62#, is shooting my 28" 394 grain A/C/C arrow at 273 fps. Since noise travels at 1128 fps it is way more important to have a bow as quiet as possible IMO. I have never heard a 70# bow shoot as quiet as a 60# bow. Bows also perform the best at their peak weight and so many guys have a 70# bow and have it turned down in poundage and are not getting the full performance from their bow like they could. Bowtechs' engineering dept told me on the phonethat their bows leave the factory at their peak and that a 60# bow peaked out will outperform a 70# bow turned down to 60#. I have seen the light with these 60# bows and will never go back.
http://www.bowhuntinginfo.com/KineticEnergyNew.htm