Sails are actually quite similar in total square footage.
They may be similar in square footage but you cannot hang an SX Main on a standard mast. You can run a standard main on an SX mast but it will look kind of funny. Batten lengths won't interchange very well. The Jibs are also different sizes and won't interchange.
To start at the beginning the comptips are the same. The bridals, furler and boom are the same. The mast extrusion shape is the same.Here is how an SX is different.
The extrusion part of the mast is longer.
The diamond wire are longer.
The side shroud are longer
Upper forestay is shorter
Lower forestay is longer
Trap Wires are 5 inches longer
The Jib halyard both rope and wire are longer.
Corkguy Currently not disclosing how many 18's I have.