The 5X is the running-shaped Ultraboost. Light BOOST replaces the old pellet midsole, so it is softer and a good deal lighter than the shoe you remember, and a Torsion System through the midfoot stops it feeling sloppy. The 10 mm drop keeps everything familiar underfoot.
It suits easy road running and long slow miles, and it will happily be the shoe you keep on afterwards, which is more than most trainers can claim.
It is not a performance shoe. At around 275 g there is nothing quick about it, the ride is plush rather than responsive, and if you want something for tempo days or a race you are at the wrong end of the adidas range.