Jeff,

The majority of our fleet uses 5MM FSE Racing Sheet with 3MM Dyneema tapered into both ends. Racing sheet is similar to the stock line on the C2 but actually a bit better.
Personally I am fine with it just on the end that hoists the spinnaker.
I also prefer using a no stretch and stronger 2.5mm dyneema in Marlow's D12 Max. It's a bit more expensive but worth it. If you don't use that I would suggest using a New England Ropes Dyneema. Marlow and NER have the best two PU coatings.
I've made a lot of halyards and sold them, I'd be happy to make you one, shoot me a PM on facebook or email me. I make them a bit longer than than the AHPC website and you can fine tune it to your set up, since everyone has a different set up. Only catch is if you have an under tramp halyard I won't be responsible if it tangles! I've never heard of any issues of Racing Sheet tangling except in these under tramp systems and I am dumbfounded by it.
-Todd