How do these compare to the XA Pro 3D Ultra? What is the difference between Salomon shoes XA series and XT serires?

The difference between XA and XT series is simple. XA segment can be described as the "mountain goat family": Superior protection and stability for usage on technical terrain, on and off trails. Because of the focus on these two benefits, the XA family is also less "runable". Why? Because of the added layers of protection on top and at the bottom. These layers make the shoe a little bit stiffer than the XT and a little bit heavier as well. There's nothing better on the market for mountain running where you have to alternate run and walk. Besides these prorection features, we have developed the XA with a low to the ground geometry to provide the extra stability you need when you are on an uneven terrain. For the XT family on the other hand, we use to call them the "trail experts family". Very performing on all type of trails, lighter, more flexible they are definitely more runable. This feeling is mostly due to the extra cushioning of the bottom unit, but also to the innovative ACS (for Agile Chassis System) which provides at the same time stability and rebound effect. Comparable to a car suspension which adapts to the terrain and the speed of the vehicle. In the XT family, you'll find the XT Wings and the lighter Hawks and Whisper (women's version of the Hawks). The main differences between XT Wings and Hawks are the level of protection (more on Wings) and the stability (same comment)

I used to wear the xa pro 3d's all the time. I bought a pair of xt wings and thats all I wear. They are so much more stable, much lighter and more responsive than the xa series. I am eager to try the xt hawk.

I don't know what the technical differences in the XA and XT series are, but I have used a pair of Salomons from each. I think that the XT Hawks are a better pair of shoes than the XA Pro 3D Ultras. They are lighter, provide more ankle support and fit more snug around the entire foot. While I was pleased by the XA Pro's, the XT Hawk's are an all around better shoe.