If the trajectory is still acceptable to you, its not hurting a thing. Graps Ive shot 860gr arrows from a 45lb bow....in fact, killed deer with 825gr this season at 15 yards. Ive went as high as 450gr heads with 45lb bows. In momentum formulas, the gain in momentum/penetration increases at a much greater rate, then the loss of velocity. There would be a diminished returns at some point, but you wouldnt be able to stand the trajectory. If the arrow is still shooting where you are looking at 20 yards and under,,,,you have not reached that point.
Here is a vid of me shooting 860gr arrows at 15 yards with 45lb bow. Grouped decent for me, and I only noticed a trajectory loss at more then 20 yards.