As a footnote to the shrinking switchback issue- I now have Ibex "Shaks" and have washed them twice in the machine and low dryer....and see no shrinking problems at all. So going to the Shaks seems to be a good alternative. (except they are not on sale of course).
Elk,
I just checked my Spinnakers and they are a size medium and fit me fine- my hips are 42"- pretty substancial. The large would probably fit me fine too. So I would think the large would be plenty big enough for you (not knowing your actual hip size, but seeing your picture on your bike...)