"Finally your halyard clutches must be able to take the new line size. My halyard tails are currently 1/2" and 7/16 ". I will be going to 5/16" and 3/8" line for my 30 footer. So you guessed it new halyard clutches are also required. Hopefully you will not need all of this but your do need to check."
I may be too late on this but I generally have an extra layer of sacrificial cover placed over the cover on smaller diameter high tech halyards where they pass through sheeves and stoppers. This does two things; since it is the covers that typically wear out on high tech line, it extends the life of the line and second it improves the grip of the stopper, or in your case would keep you from going to a new stopper.
The trick is to buy cheap dacron line and strip the cover. I have not done this myself but I understand that the trick is to make a 2 foot or so long circular fid out of light gage electrical conduit. The cover from the sacrificial line is stripped onto the fid and then slip off onto the high tech line where you need it. The ends of the sacrifical cover are tucked through the cover of the high tech line at each end and then stitched into place.
One other point, since you can generally use smaller diameter line with high tech stuff, the price often ends up being close to stretchier low tech stiff.