The XT stands for "Xtra Tough" and "Xtra Traction". This disc has added grip and is super durable, meaning better wear and scuff resistance.
The Roc is Innova's most popular discs among pros, it is stable at high speeds and slightly overstable at lower speeds. A great all around, goes where you throw it golf disc. Good into the wind. This is one disc that gets better as it ages.