I blew through an bull elk like a hot knife going through butter with a 512g. Easton Axis arrow and a STOS broadhead out of a 64lbs. DAS bow.
It's not conclusive evidence...but this was the lightest set-up I've used.
I've used 720g. Grizzly Stiks with a Shkote broadhead and 640g. Easton 2419's with Ribteks shooting a 69lbs. Black Widow and got less penetration with the heavier arrows.
All bulls were between 15 and 20yrds. broadside.
I'm sold on skinny carbon arrows for better penetration.
You have plenty IMO to easily kill an elk.
Ray