Warpspeed is the strongest, least stretch line available at the time and is probably the best choice for most sheets, including main, jib and spinnaker.
While 3/8" is usually recommended, 5/16 will do the job even better, particularly if you use the new Harken Carbo Ratchamatic Systems.
I just put the 8:1 system on my Taipan 4.9 using 3/8" Warpspeed (should have used 5/16) and the line runs very easily through the block system.

Also, just replaced the Harken cleats with a Spinlock and that seems to work really well also. Getting the right angle was important so you could snap the sheet in and out while on the trapeze.
So far it all works much better than what I was using before.
By the way, this site is now carrying all of those items in our OnLine Store. (Ad Police: This is my site, you understand )
Rick