Hi Dave,

Hope you are doing well!  

Lots of complex questions...

If you go with a hybrid fabric that is designed for a crosscut sail, the difference between the cross cut and the triradial will be small, but still real. I very much doubt anybody has real data, just opinions.  There is a lot of confusion between the short term shape stability of the sail, long term shape retention, and just the mechanical strength of the sail. 

The triradial cut will have much better shape stability under load than the crosscut.  On the down side, since they are almost all made with single stitched seams, they take a bit more maintenance.  Since the seams are now parallel to the force, they tend not to blow out, but they are still subject to chafe and occasionally need to be restitched.  

Certainly the triradial cuts for both genoa and main have proven themselves as suitable for furling.  I would NOT step up the weight of the sailcloth above the original.  That will just compromise the light wind performance for no real benefit.  I don't know of anybody who has torn out sailcloth of the recommended weight.  Failures are almost always seam failures that can be prevented by inspection and repair before failure.

Sails of any material (except laminates!) will lose shape long before they fail mechanically. I very much doubt that ANY sail after 25,000 miles of tropical cruising will be "like new" in performance. Genoas can be nursed along--at a significant performance cost, but older stretched out mains and mizzens will start to give you furling problems.

The advice we got from our sailmaker was to go with radial cut for performance, and use Dimension Polyant ProRadial fabric at about a 50% savings over HydraNet.  His opinion was that the ProRadial would show similar lifespan, and would have a bit less short term shape stability.  In his opinion, the Hydranet would be his first recommendation for a racing boat that didn't go with laminate, but he felt the benefits for a cruising boat were minimal. That's the direction we went, and have been very happy with them.  They were a dramatic improvement over the dacron cross cut sails the previous owner had installed.  Would we get 50% more life if we had gone with Hydranet?  We'll never know.

Our cross cut mizzen from the previous owner (also dacron)  was baggy enough that furling was getting fussy.

By far the most important thing is to be sure that the sailmaker either knows what an Amel sail is supposed to look like, or carefully copies what is extant.