In the mountain roads leading up to and down from Jerome, Arizona, we find the AJ-V8 at its most delightful between 3500 and 4500 rpm. The intuitive paddle controls make it easy to keep the revs in the pleasure zone. Jaguar claims the adaptive, six-speed ZF box, which has normal and sport modes, is the fastest shifter in the business. Who knows? There's so much horsepower out there nowadays that, while the new XK certainly feels fast enough, it's not what you'd call brutally fast. For that, we await the upcoming XKR.