Go with the 50. It will shoot just as far as the 45 and carry more energy to boot. The 50 will burn the mag charges better than the 45 will just like a 338-06 will shoot a 200gr bullet faster than the 30-06 will. The larger bore will allow more powder to burn before the bullet exits the barrel. Also if you are ever going to use it to hunt elk or moose the minimum might be a 50 cal. I know it is here in colorado and probably other states too.