It is covered 12 strand SK75, should be comparable.

Well, I have pre stretched them with about 300kg 10 times. Than put them on the boat and streched again. After one week (without sailing, but mast up and tensioned) I went sailing (strong winds) and after a few minutes they were stretched another 6cm. At the end that means the windward forstay and the main sheet has to take nearly all the load). Back on the beach I had to tension again. That is what I meant with "difficult to tension".

Regarding stiffness, it depends on the rope diameter of course. If you select the diameter by breaking strength (equal diameter for wire and D12), D12 will stretch 1% at 20% load and wire 0.2% at the same loading, hence wire is 5 times stiffer. To get the same stretch, you have at least to double the diameter. However I don't know how important shroud stiffness is, if your boat is conventional rigged (left and right shroud + one forestay). However if you have two forestays, it plays an important role.

If I have to re-tension again after the next sailing or if the leeward forsetay constantly comes slacky, I will switch back to wire <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />.

Cheers,

Klaus