Spinnaker sheet selection

[Curryhouse]

I have a symmetrical spinnaker that came with the boat. However I do not have any sheets. Researching, I've found general info that indicates 8mm double braided line would be suitable. Lengthwise, 1.5 - 2 times boat length. For those TH owners that use a symmetrical spinnaker, does this info seem correct? If not, what size/length do you use?

Thanks in advance.