The weight carrying ability of the hull seems to have been superseded by what you can do with the rig. Designs like the CT were originally thought to be exclusively the territory of light weights (IE sub 22 stone) and nowadays seem to be sailed fast with significantly more weigh aboard. It may well have always been the case but the good sailors in the class were lighter in the 90s?
Even flattening out the rocker line incrementally doesn't seem to have made much difference. The modified Mk4 with the fuller bow has been reported to be less weight tolerant but I'm not sure this is borne out by results and there are not that many of them around.
The Genii seems to go well with larger sailors aboard (Nick Craig/Alan Roberts, JT and Richard) and I'm not sure we've seen a proper campaign in the hands of a recognised lightweight team from this hull. So we don't really know what its weight range is like other than it's a match for its older stable mate.
We know what weight Keith's boats were designed for, but this doesn't always correlate to what happens. A class elder once commented that it seems every time someone designs a hull to carry weight they end up carrying less........