I know this an older post, but thought I'd confirm the answer. 5 turns from max poundage is all you should go. I called Mathews today. A pretty well known and respected 'tech' told me I could take my 60# HeliM down to 48#'s. Rather than take a chance, I thought I'd call the factory.
They told me if I needed to go below 50# draw I should consider getting 50# limbs. Told me not to shoot less than 5 turns or 50#s.
Could you get away with it? Maybe . . . but I'm not taking the chance.