RE: 85 or 100 grains?
It'll be faster, of course, but will require changes in your setup to keep it in tune. The arrow will act stiffer with a lighter head.
You may be able to make corrections with a simple adjustment to your rest or draw weight, but it may mean new arrows if you are already using an arrow that is on the stiff side for your bow setup.
It will also mess with your FOC %. That's a whole other discussion.
Good luck.
If you have troubles, or want to get a better idea of what to expect before starting, spend some quality time over in the technical forum and give specifics when you ask.
The end of deer season is an excellent time to make changes.
That way, you're all good to go long before it comes up again.