For most tasks, the Dell XPS 12 will feel faster than your existing machines. But it has Intel HD 4000 graphics and no dedicated graphics, so it's not really a gaming machine. You'd have to go with low settings and 1366 x 768 resolution to get just 30 fps in several of the games you listed (particularly Skyrim and Need for Speed newer titles).
12.5-13.3" Ultrabooks rarely have dedicated graphics, and if they do (like the Asus Zenbook Prime UX32VD), they're fairly low end. You'd have to look at a larger laptop like the 15.6" Samsung Series 7 Chronos to get a touch screen and decent midrange dedicated graphics for gaming.
-------------------- Lisa Gade Editor in Chief, MobileTechReview