I wouldn't go below 60 with it. The bow wouldn't have the proper amount of tension on the string and cables, so your performance would suck and the bow would be noisy. Just bite the bullet and buy the 340's. Find someone shooting 55 or lesspounds to sell the 400's to. Or maybe a trad shooter would take 'em off your hands.

If you're concerned about string/cable break-in, then measure your brace height and axle to axle length. If brace height is more than 1/2" lower than what the specs call for, or axle to axle length is more than an inch longer than spec, then the string/cables need to be twisted up and adjusted.

If you're using stock Hoyt/Reflex string and cables, I can practically guarantee they need adjustment. They are the worst!Put some aftermarket rigging on the bow, ASAP.