Don't forget Dyneema usually means SK75, which is usually considered too stretchy and creepy for most rigging applications.
Chemistry (not rigourous):
Dyneema/spectra is polythene pulled out so the molecules are more lined up and I think the polymerisation process may be better than ordinary polythene so you get more carbons in each chain. Each unit is a carbon and two hydrogens (CH2).
SK78 is 500,000 of these, which is 15% of a mm long (this is my own calculation, not from a source, so may be wrong)
Presumably SK75 presumably is less, SK90 more.
Antidotes uppers are 3mm SK78. The lowers are 5mm SK78. The D2s are 3mm SK78 but 5mm may be better.
The forestay is 3mm wire (though could be SK78 or probably SK75, and people have made these from vectran too), as are the shrouds. This is really because we lacked the bottle to keep the mast up with rope.
The shrouds are 3mm wire, and 3mm SK78 is far less stiff than this, though 5mm SK78 is about as stiff as 3mm wire. I asked Davro whether people use 3mm wire for its strength or its stiffness, and the historical message seems to be that there were many breakages with thinner wire shrouds. This suggests it is the strength of 3mm wire rather than its stiffness which has made everyone standardise on this in recent years, though thinner shrouds may also have been too stretchy of course. In turn this suggests that, because 3mm dyneema seems to be stronger then 3mm wire (~600kg vs ~1300kg in our test), then 3mm SK78 would be ok for shrouds.
That said, we were not too happy with holding the mast up with rope that thin. We bought a load of 5mm SK78, but is so huge I don't think that is suitable. Not wishing to seem like a fudger, if 4mm SK78 exists then it would seem like a good compromise!
SK78 (CH2
