What do you do when you are on the boarder of 340's or 400's depending on the broadhead (75 or 100 grain) you shoot?

A majority of the recommendations on Easton's site say I should shoot 340's. A couple of archery shops tell me shoot the 400's.

I am up in the air. The 400's are knuckle balling at 35-40 yards. Will the same happen with 340's or will it get better or worse?
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