Speed makes any bow less forgiving. No if's and or buts about it. A heavy arrow will always shoot better keeping everything else the same. I believe that as long as broadheads and field tips hit the same spot broadhead flight will not be a problem. If broadheads and field tips are not hitting the same spot, there is a problem with either nock height, or arrow spine.

I have seen guys shooting 70lbs, that couldn't shoot through a hog @ 7 yards. If your BH and FT are not hitting the same spot your arrow is coming out of your bow crooked. On a close shot this will kill penetration. IMO having broadheads and fieldtips hitting the same spot is the only way to maximize accuracy and penetration. When my BH and FT are hitting the same spot I have never been able to get better groups at 50 yards.