I'm not sure how light you are talking about, but there are a lot of factors to be considered.
For one, I think the laminated limb bows can take a lot more punishment than solid limbs.
Look at Hoyt's limb tests. They dry fire a bow , what ...10,000 times.
Also HC lets you shoot an arrow down to 3gr/lb. and still warranty the bow. Again Laminated limbs. Barnesdale's are one of the best out there.

I wouldn't be afraid to go slightly below 5gpp at a lower poundage like 60 - 62 or less. But I'd be afraid of the strings blowing off my bow at 70lbs. w/ too much less than 5gpp. It's not so much the limbs , but the result when the cables and strings let loose, and cause reciprocal damage.