Hi Andy,
40lb single strand wire is what i have used on all of my boats. Same Malin Stainless steel leader wire brand i use for shrouds and backstay.
The issue with dyneema and before that dacron on leech lines is the amount of stretch under load making minute adjustments difficult and any setting moving under different wind conditions. Near imposible to get repeat consistent adjustments.
Just loop ithe wire at the top over the hook that goes into the mast and put a loop in approx 100mm above the jib boom that leaves enough room for a dyneema and bowsie adjuster at the bottom.
Cheers
Brad