Here is the 23 sq m sail I had on Blue Moon, which was built from Weathermax 80, which is 8oz.  The winds was only blowing about 12 knots and it was setting well.

Perhaps if it had been 60z might have inflated a little more in these light winds.  On the other hand, this sail, built by Paul Thompson of NZ, was bullet-proof!

Click on the mage for a larger view.

Andrew wrote:

Question: would it be overkill to make the top panel of a junk sail out of 9oz ‘storm sail’ Dacron? Could you make each set of lower panels out of lighter and lighter fabrics as well?

It would depend on the size of the sail, but I think the general principle is sound.  For a 30-35 sq m cambered sail with a fan-shaped top and seven panels, I think the top three panels could be 8oz, with 6 oz below that.  Maybe even 4 oz for the lower two panels.  For a moderate to heavy displacement boat, you could maybe have 10% camber in the lower two panels, then 8 % for the next two, then 6% for the next two panels of the fan, with 4% for the top panel.  I have only ever had the same weight of cloth for all panels, but have thought about this approach.  Your lower panels are your genoa!