Sailaway...I'm afraid I'm with Trayfors on this one. You need lots of give in your dock lines to reduce the shock loading. I would think that the dock line manufacturers would know about this and there is a reason New England ropes recommends nylon and ALL of the made up dock lines West carries are nylon etc. etc.
If you think you are right about this as I'm sure you do...how about some links to credible sources supporting this approach?
Here's one for my point of view!
http://www.boatus.com/boattech/casey/21.htm