[Since the 125gr judos fly great with the 2016's, wouldn't 125gr Snuffers likely fly good too? Is a 457gr arrow enough for heavier game like elk?
Shooting fixed broadheads could magnify a problem. The 2016's IMO even with 125's fields or judo's could (remember could) be underspined, however, your fletchings are able to counter the problem by stabilizing the arrow. Have you tried bare shaft tuning with field points? That would be the best way find the correct arrow shaft.
In your second question, you are only getting about 7.5 grains per pound on your setup which is light.