How many beach cats out there have completely taught leeward shrouds when you are sailing to windward?
If it isn't completely taught then you can use dyneema (I would use ultrex) for the stays as long as you build in less length to allow for creep. Once the creep is out there won't be much more lengthening. It isn't like the line continues to get longer and longer because of the creep- it stops eventually. I made a ultrex 5/32 forestay (the top "pigtail" as I call it that then attaches to the two lines going to the bow tangs- boat doesn't have a jib) on an 18HT and yes, it was a little guessing as to how much shorter to make the line when doing to eyesplices but ti works fine. One thing I try to do is make sure I pull the line out as hard as I can before doing the splices.
As Mike said though- dynex would probably be best but $$$. My f31 has 3/8 dynex dux precourt shrouds (breaking strength something like 27,000 lbs!!! a little excessive)