I have two quilts that I did with the Hobbs wool. I've machine washed and dried both several times and they still seem beautifully fluffy and soft. I would say the 3-5% shrinkage that they quote is pretty accurate.
Actually if you look at the package inserts in both the Hobbs and the Quilters Dream wool, both suggest hand washing and line drying. I was terrified the first time I machine washed the Queen size one. I wash the wool batted quilts in warm/cold on gentle cycle with a smaller amount of detergent and then tumble dry on the medium setting. So far so good. From my knowledge of wool; hot water, alot of agitation and soap is what makes wool felt. So as long as you stick with cool or warm water and the gentle cycle you should be good.