The BC on the 100 grain is higher than the 80 grain, so the 80 will lose velocity faster, and at some point the 100 will catch up to the 80 velocity wise. My guess without calculation would be that would happen before it reaches 400 yards. If your rifle shoots satisfactorily with the 100 grainers that's the way I would roll.
"Before you criticize someone, walk a mile in their shoes. That way, you'll be a mile from them, and you'll have their shoes."
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