100 grain is a good weight for your set up i think with a 75 grain fixed you would have problems getting proper flight, tune your bheads make sure they spin grab them by the knock and spin them if you have a little woble take them at a little bit of an angle apply a little pressure and spin again if you need help broad head tuneing dont be shy fixed blades can be hell to get to fly with field point but a few adjustments should get you real close good luck