Hello guys, this is my first time posting. I am getting ready to order my lift and I am having trouble deciding between the 2865 and 2866. I like the idea of a progressive spring but I am confused, on the spring chart it says the 2866 is 10 mm of lift vs the 2865 is 40 mm of lift. Can someone please explain the differences and also the pro's and con's of each. Thanks.