That will answer any concerns you have about strength and will also reduce stretch. The downside is of course, cost.

If you can get the right length it will help you avoid overspending. A diagram with all the measurements between blocks would help you add it up, but might be difficult to re-create yourself if your boat's laid up for winter. If you can't get it from the boat maker I'd wait till after you can mark and measure the line that's in use now.