We got our hands on the all-new 5.0-litre Jaguar XJ LWB for a first drive in the North West this week, and found a car that does for luxury saloons what the XF did for execs...I first saw the all-new Jaguar XJ 'in the metal' last Summer at the Jaguar design studio, where the new luxury saloon's designers talked a group of journalists through the car's inception, heritage and raison d'etre.Eagerly-awaited, following the new XF, the XJ aroused a certain amount of controversy for its Beyonce-like booty - a huge backside designed, no doubt, to swallow 34 sets of golf clubs.I'd been ambivalent prior to seeing the car at Coventry, but seeing the car first hand made all the difference - this was a car that really hung together, more than the sum of its parts.Taken separately, that large rear, the floating roof, the interior designed to bring to mind a boats, the virtual dials may not have made sense. Some suggested that the XJ had wandered too far away from its traditional 'three box' roots.The new XJ is what the XF is to the S-Type, a total reinvention with just enough DNA for buyers to make a mental connection back to previous models. There's little in the lines and shapes of the car, but it's there in the intent: the power, sleekness and luxury. All slightly understated and reserved, barring the face, which is noticeably more aggressive than the XF. A statement of intent.The car is a looker inside and out, and Jaguar has taken the new XJ away from the perceived luxury saloon market. Whereas Mercedes, BMW, Audi and Lexus were traditional foes of the old JX, this new XJ appears, in terms of design, to be closer to Maserati territory. There's something rather grand tourer-like about it.A spin in the long-wheelbase XJ, powered by a normally-aspirated 5.0-litre petrol engine does nothing to convince me otherwise. The Jag is tech-heavy, luxurious, spacious and refined in every way, though there's not much opportunity to put the XJ to the test on the roads around Greater Manchester.The gently-burbling petrol engine hints at the power behind the smooth cruising, and the drop-down provides the same smooth acceleration as the XF's powertrain.Around town the XJ feels far more nimble than a car as big as the Jaguar should; but there's nothing approaching twitchy or manic about the way the XJ transmits the vast amounts of power and torque the engine puts out.The interior is everything you'd expect from a Jaguar saloon, but now there's cutting-edge gadgetry sitting side-by-side with the leather and the walnut trim. There's a Bose audio system with 20 speakers, rear parking camera and sensors, keyless entry and ignition, blind spot, collision warning, adaptive cruise control, connectivity and a host of driving dynamics that can be altered to the driver's content on the Portfolio model I tested.And as this is a long-wheelbase model it's limo-like in the back. There's huge legroom for all passengers, and quad-zone climate control. Spec it out with DVD players in the back and all four can travel in comfort and style.There's also the icing on the cake. The rising virtual dials and the dual-screen that shows a satnav to the driver and DVD to the passenger. Outside there's the cat-claw rear lights and the leaper taking pride of place. Little details that come together to make the new XJ much more the sum of its parts.It's a Jaguar XJ, but not as we know it.