On the Calculator,there is not much change in KE with the 3 heads,with such a low DL and DW.So I probably would stick with a 100 gr.
Should I use the 82g broadheads to get a faster arrow speed or heaver ones for more energy.
What effect will the weight of the broadhead have on the arrow balance?
Heavier will give it better FOC
Probably a little
Will there be much difference in point of impact with say the 82 or 100 g heads.
As long as your bow is tuned ,your BH should hit the same point or very very close,
And finally I use the same arrows for field shooting with a 100g point should a 100g broadhead have the same point of impact
Here is a link for BH tuning to help.