Re: rope & wire halyards vs all rope halyards
There is no question about replacing with all rope. Just do it using the same diameter as what you now have. The new line will certainly be stronger than what's there and will fit your hardware. Your masthead sheaves will most probably accommodate the line without modification but check it out as others have noted. In our case on both our Sabres, the sheaves were in good condition. If aluminum, they don't usually fail unless badly neglected or something is eating them (like countless meathooks)
Unless you are racing, I'd recommend VPC or Samson XLS. I would not use StaSet-X only because it's a difficult line to splice.
Sabre 38 "Victoria"