StaSetX is a great choice for halyards, and the Sta-Set is a good choice for for the sheets.
I disagree with Dog on StaSet X. I find it stiff, does not like winches and pills horribly and is still quite stretchy. I have had it on two boats and will never use it again. You might try to find some New England Ropes VPC.
Contrary to popular belief StaSet X is also still fairly stretchy compared to other halyard line. It stretches 2.4% or 14.4 inches in 50 feet. My halyards are 120 long.
I like StaSet for sheets but if you are racing in light air the stay set can get awfully heavy and weigh down the sail..
Unfortunately most US sailors use NER mostly because there was a family connection / relation between the owner of New England Ropes and West Marine. It's unfortunate that many sailors have only had access to NER when there are plenty of other less costly options. Unfortunately this relationship between WM & NER has forced companies like Yale Cordage to persue other markets and put very little effort into the marine market. It's too bad because Yale makes some great stuff as does Nova Braid out of Canada.. NER has been sold so it will be interesting to see how long this "relationship" lasts!!
Other alternatives to StaSet X:
= 2.4% stretch and is about $86.00 per 100ft for 3/8" (Best source Hall Spars).
Nova Braid XLE
= 2.25% stretch and is about $70.00 per 100ft for 3/8". (Best sources is Rope Warehouse or Cajun Trading Co.)
= 2% stertch and about $86.00 per 100ft for 3/8". (best source usually Defender)
= 1.65% stretch and about $89.00 per 100ft for 10mm (roughly 3/8"). (best source Defender)
Samson XLS Extra
= .7% stretch and about $133.00 per 100ft for 3/8" (best sources Hall Spars, Defender or Annapolis Performance Sailing)