I recently bought a Atmos tour Spec HY 85g X stiff shaft for 915HD Hybrid. It has changed the swing weight drastically to the point of unusable. Is the head weight that much deferent in the new 818 where it is a good swing weight. I noticed titleist is now using the the same shaft in the new hybrid, so I'm guessing the head weight is far heavier? If so, can someone suggest how much weight to add to my 915 head to create good swing weight?