http://shop.sailboatowners.com/cordage/list2.htm?bid=633&cart=13842369851332467&action=up

You will see that if you take the "normal" load, you get your recommendation of the lighter shackle. If you click on "stormy or windy" button you get the heavier Wichard. Mirror, mirror, on the wall....

I'd go with the larger Wichard unless you are not going to be taking the boat out into anything snotty, ever.