Re: Optimal halyard length?
As Faster said halyards run back to the cockpit or left at the mast is really an item of personal preference. If you run the halyards back to the cockpit then you also need to run the reefing lines back to the cockpit. There is a pretty good chance that your boat is setup to use a boom mounted reefing hook for the reef tack, and if so moving to cockpit setup reefing is a bigger rigging project. I have everything run back to the cockpit on my boat and have plans to move the spinnaker and jib halyards back to the mast.
Someone pushed back on my suggestion of dyneema halyards. I was suggesting them because they will allow you to use existing wire-halyard sheaves. Wire halyards on your boat were probably 1/8", and 1/8" dyneema is strong enough for the purpose where 1/8" double braid is not. If 5/16" halyards fit on your existing sheaves then there is no reason to use dyneema, though a dyneema-blend halyard (XLS Extra or Sta-Set X) is a nice upgrade with much less stretch for only a little more money.
You might want to check your local West Marine's clearance section. The one here in Seattle is closing out some pre-spliced 5/16" x 70' halyards for a good price. That is probably a little long for your boat, but you can cut off the tail and use it for other purposes (like a preventer).
boats that I sail on regularly: Pearson 28-2, Rondar 505, Yankee 30, Blanchard Junior