I have just the progressive rear spring on my stock OEM shock, not the entire Progressive 465 adjustable shock (due to the big difference in $$). Just the spring provides an improvement over OEM and was noticeable to me. From other reports I've read, paying the extra money was worth the improvement noted. So the full shock and spring is on my wish list.
If you just go the spring route, make sure you have someone that can do the spring replacement. Getting the old one off and the new one on is not for amateurs.
2008 Yamaha V Star 1300 Black Cherry