I got to spend a short time with my buddy's B-Day present, a St. Croix Avid X spinning rod, all I can say is I'm getting one!!!!!  The rod is sweet, but I'm trying to wrap my mind around why this rod feels so much different from the regular Avid.  I picked up and fished with the 6'8" M-XF Avid and then after 20 minutes and 1 small fish I used the 6'9" ML-XF and I did not want to put it down. Now, I do understand that one was a medium while the other was a medium light but I also got to use the medium in a 7' and liked that too!!! My friend and neighbor is a St. Croix fanboy, he has a few Avid series rods, in fact most of his rods are Avids and he went an sold an Avid spinning rod and got 2 Fenwick ET Smallmouth rods after using mine. Now after they released the new Avid X he went and tried one and ended up buying the 7' medium and just got the 6'9" ML-XF for his B-day and this is really making my wonder why a rod with the same blank with some cosmetic changes and different guides can have such a dramatic difference in feel, it is just really strange. What I want to know is if anyone else thinks these rods feel better or different from the original Avid, I mean to me the difference is night and day and I'm wondering if it is in my head or if I'm not alone, I'm interested in reading everyone else's views on this.

Assuming the blanks are the same, my guess is the micro guides and split grip are the difference.  The split grip will change how the rod balances and overall weight of the rod.  

 

Any time I go from a rod with standard guides to a rod with micro guides, I can tell an immediate difference.  Rod blanks feel so much lighter and more responsive with micro guides.  It makes a huge difference for me.  I don't have as much experience with spinning rods but with casting rods, this is definitely the case.

 

Of course, if the X series uses different blanks than the Avid, that will play a large role as well.

The X series uses the same graphite but the build is obviously different. The split grip and micro guides will definitely impact the feel in your hand.  I felt same type of reaction when i used an Avid and then a Rage, same graphite (rolled in a different location though).  A rod and it's feel is a lot more than the blank though as i think you are experiencing. 

I have two 7'mediun light avids. One factory and one custom with recoil running guides and split grip. They fish different. The custom is much more sensitive and lighter. I would say the guides and split grip are what is accounting for the difference you feel. Especially keeping weight off the top half of the blank will make a big difference.

Probably because St Croix finally figured out how to hide the threads for the lockdown nut.