One Oceans Kayak did some tests years back which is commendable for the building community.

http://www.oneoceankayaks.com/Epoxtest.htm

However, I don't think the differences amount to anything that is going to make or break a project. Many people choose something that they can afford or get easily, WEST is 5-1 and almost all the others are 2-1 and that's something you have to consider.