Snowdrop,
As mentioned on your other post, I also have a
bowsprit setup with a Karver K5
furler. I also went through the decision making process in
buying a new sail wardrobe a couple of years ago. This is what I decided and what I have since learnt.
My intended use for the sails is inshore cruising with a fast-approaching goal of long-term
offshore cruising. Although I obviously want the best speed from my sails, I'm not
racing anywhere and a big consideration was ease of use. For winds of 13kts+ I have the standard genoa and main. My biggest
learning curve related to lighter wind sails. I was happy to restrict my additional wardrobe to a sail for mainly downwind and a sail for mainly upwind sailing. Having done my
research, I went with a deep cut asym spinnaker and for upwind, I went with a screecher. The screecher is cut like a big genoa and attaches to the
bowsprit with a torsion line sewn into the luff. I decided at the time to go with a heavier material for longevity and had it made from 3.8oz dacron. (Sorry, I gave you wrong info. on the other post). It works great and it's super easy to furl by hand even with a bit of wind in the sail. However, as I had it cut with a heavier cloth, as you are considering, I found that it wasn't significantly different from my big genoa and only filled a small gap in my wardrobe of upwind sailing in the 5-12kt range.
Last year I purchased a code zero. An enormous great sail made from 2.2oz nylon. It has a torsion line sewn in the luff. I really love this sail and it has become my go-to sail in light wind. It deploys and furls just as easily as the screecher, both of which are night-and-day when compared to my mis-behaved asym. The biggest difference with the code zero is the range at which I can use it...let me explain.
I'm only brave enough to use my asym in wind up to about 17kts and I found that when I used it at wind angles of say 140 degrees, the boat would pick up enough speed to push the AWA forward so that I was practically sailing on a beam reach. Any wind forward of around 130 degrees would result in the apparent the wind coming forward of the beam. Although the code zero isn't designed for running, it practically achieves the same thing whereby the apparent wind quickly comes around to perfect angles for the code zero. On top of that, the code zero is still happy to sail up to around 50 degrees in light wind with a tightened luff.
Therefore, unless I know that the wind is going to be at my back all day, or I'll be close reaching all day, the code zero is always the go-to sail in light winds. At 2.2oz, the sail is quite happy at TWS above 15kts but its such a big sail that at that speed my conservative side kicks in and the genny comes out. So, to answer your question, as others have said, unless you're really going to push your boat to its limits, there's really no point in going with a code zero made from heavier material.
I'm not expert, I'm just telling you what seems to
work for my boat.