Our original main halyard was 6mm braid on braid, so I am pleased to hear it is a higher spec. and less likely to jam between cheek and sheave of that top block.
Have just replaced our main halyard with sk78 dyneema with 24 braid cover, Racing dyneema equivalent, bought in Spain at a ridiculous 2.80€/ metre.
25 metres is good length. I skimped on my last one, thinking I would save another pile of string in the cockpit, and then found when the mast came down in place for trailering, I had not left enough for it to stay in the clutch etc. Only a bit of a faff putting back through, but when you have wrestled the mast up and got all sorted a pain to have to do that as an extra.
Incidentally, picked up a Calor Gaz 907 replacement bottle for 22€ at the same shop, we don’t half get ripped off in this country!