I was just going to copy the current length, but your method may prevent too much extra. I think I'm at about 72' right now which leaves about 8 feet to coil once I've stowed the main.

I suspect 6mm line would be too small for the rope clutch I have. The 5/16" I'm using now has an additional cover attached right where the clutch grabs to keep the halyard in place when tensioning the downhaul/sheet.