Phill,
Yes, of course, I consider other number, basically customized B Class numbers:
For the sail area, as the boat is quite light,we have a virtuous circle, not too much sailing area is required and it becomes physically affordable for seniors, even in long distance race. So 21/22 square meters seems to be reasonnable for a 140 kg (310 lbs)crew, and bigger sail area for heavier crew, until 24.5 square meters for instance)
For mast height, I target something about 10.5 meters in 2 parts with the junction at the spreader level, in order to have a 6.4 meters parts + a 4 meters parts, for easy storage purpose, also it means the hound will be at 8 meters height.
For the crossbeam width B Class rules are OK, around 3.1 meters.
About the jib, I agree with your argument, but I think the heavier the boat, the more this argument holds.
Long talks with the HOBIE TIGER designer, MR J Valer have provided me another view, the lighter the boat more the relative importance of aerodynamic drag increase, and therefore a split rig (jib+ main) providing hight lift seems not optimum for light boats.
A Cat are quite fast in long distance races, as long as spinnaker is not required.

Thank you to mention that 140kg is achievable for home builders with a single main sail plan, also it is cheaper.

The basic idea is to concentrate the technology where it is most efficient ( mast for obvious reasons) and curved pierce-wave croosbeams because it will provide additional degree of freedom for hull design(ie: curved means that the middle of the crossbeam is higher than at the hull junction, so for the same freeboard the hull designer can move the rear crossbeam aft, and get the same clearance above the water.
Or lower the freeboard or a mix of both.
If the crossbeam is piercewave with an elliptical section at the hull junction( 3.5 / 1 lenght/height ratio)the drag coef can be 1/20th of the basic circle section), so you can lower the freeboard significantly and save weight, or use a cheaper technology for the same weight, or put more stuff per square meter and build longer lasting hulls.
Also no jib means fast preparation between the road trailer and the water.
In fact I seek a big A Cat for my light girl friend and me.

Cheers

Erwan