Hi John
I weigh around 75kgs and have a MK2 Landy mainsail. After racing in moderate to strong winds and advice of John Pearce I took the decision in 2007 to have Grant Piggott re-cut the Luff to flatten the sail. Now the max curve of the Luff is 90-95mm. I feel I am more competitive in stronger winds but have to be really careful in the lighter stuff in regard to sail tuning. So I think the newer Landy mains are a great sail for the heavier single hander and two up crews. However, Grant's mains are obviously very similar in shape to the Landy with just a little less foot length and slightly longer leach.
I guess we have a slight difference of opinion but that could just be because of the difference between the MK1 and 2 Landy mainsails.
As for Grants sails being better for 2 ups & heavy weights I'm not aware of any 2 up teams using them at present.
P.S Grant made his first F16 Kite for me using the measurements I supplied and it's hot.