I am shooting #58 r/d longbow that i shoot the a 100 grain insert and a 125 grain tip that if i don't release it perfect still seems to be stiff. In my opinion, it should be too stiff, but a lot of factors can make it still fly well. If you have a really smooth release that helps, if the bow is cut past center to where the arrow is actually center shot. If i were you, i would try to find some insert weights. I know with goldtip arrows you can buy 20 or 50 grain insert weights to test and see how much weight you would need to add.
My best advice, buy a field tip test kit from 3Rivers and see what you come up with. My guess would be that you need about 100 more grains up front, but that's just a guess!