I've done the math on this topic and discussed it with Greg Goodall (AHPC) himself.

3 mm dyform on the standing rigging is fully depenable.

3 mm 1x19 is pushing it a bit, Greg said any less thickness or several loose strands; you will break it.

In my math it turned out that the forestay is by far most heavily loaded. Moreso the sidestays. Think roughly 600 kg versus 450 kg. This means that a 3 mm 1x19 (break = 720 kg) could be used for the sidestays with a 50-60 % safety margin. This may sound like alot but is minimal in conventional structural engineering. The forestay and bridles must then either be 4 mm 1x19 (1285 kg) or 3 mm dyform (920 kg), given safety margins of respectively : 215 % and 153 %

If you are singlehanding then you may risk using 3 mm 1x19 for the forestay and bridles as you will be running with less mainsheet loading here.

Personally I never change standing rigging every year or season. On all my boats I used the standing rigging for 5 years or more. On my F16 (modified Taipan) I have now been sailing with 4 mm 1x19 rigging for over 2 seasons.

Greg mentioned to me that they have run older imperial 3 mm 1x19 wires on their earlier boats and that held up well. But it must be remembered that these wires were actually a little larger then 3 mm in diameter. More something like 3.2 mm. You can't this wire anymore and METRIC 3 mm 1x19 wire has a lower break strength then these older versions. I know a few Taipan sailor still using this older wires for several years now.

So in summary, consider METRIC 3 mm 1x19 as the absolute smallest safe diameter. To be really safe opt for 4 mm 1x19 or 3 mm dyform. If you opt for 3 mm 1x19 make sure you inspect your rigging often and thoroughly. If you can find some older EMPIRIAL 3 mm 1x19 (3.2 mm) then consider yourself lucky and go for that.

I hope this helps

Wouter