It's one of the most delicious, desirable cars we've ever tested, leaving little to the imagination.
If you could think of ways to improve it, the last thing to spring to mind would be that it needed more power. Jaguar has delivered it anyway.
Enter the XKR-S, which takes that snarling supercharged V8 and turns it up a few notches. The result is a car that pumps out an unconscionable 405kW and 680 Newton metres and which resides in the true supercar performance category.
In just 4.4s - less time than it takes to tie your shoelaces - this car will flash you past the speed limit on its way to a top speed of 300km/h - at which point only an electronic speed limiter will prevent it from going even faster.
The acceleration is pulverising - pinning occupants back in their seats as the massive rear tyres scratch and scrabble for traction. It's the kind of performance you would rarely have the chance to use.
The XKR-S is an exercise for doing something not because you need to - but merely because you can.
It also costs a jaw-dropping $340,000 - a full $100,000 more than the sublime XKR - for which price you get precisely 9 per cent more power and 8 per cent more torque - plus an uncharacteristically overt body treatment.
Jaguar notes, somewhat pointlessly, that the XKR-S sips only 12.3L/100km on average - and its emissions are "less than 300g/km".
Less than an Airbus A380, too, if you're wondering.
In some ways the XKR-S ceases to be what made the XK so special in the first place - beautiful, sporty yet somehow an expression of classy understatement. The XKR-S is about as understated as golfer John Daly's wardrobe.
A large aerodynamic wing across the XK's once-shapely rear end is necessitated by this car's thunderous power and fearsome acceleration - to keep it from taking off.
The car also sits 10mm lower than the XKR and has firmer suspension and a stiffer chassis.
Its electronic dampers monitor and adjust the suspension settings 500 times every second - keeping those massive low-profile tyres glued perfectly to the pavement.
There's also a body kit around the front and sides which leaves it looking more like Mad Max's V8 Interceptor than the elegantly-sculpted car from which it is derived.
The aggressive look is accentuated by our test car's all-black presentation - black paint, huge black 20-inch (50cm) "Vulcan" alloy wheels, black grille, black trim. Black everything.
Jaguar calls it "a bespoke aerodynamic package" - developed using "computational fluid dynamics". I call it "black" and "scary".
The XKR-S's $260,000 price also gets you absolutely huge brakes - 380mm on the front and 376mm on the rear - which stop the car like you've reached the end of a very long rope.
A performance-active exhaust - which in effect opens the car's throat quicker when you demand full acceleration - both enhances its performance and the incredible sound it emits.
The performance improvements on the XKR-S were developed by Jaguar's ttest and engineering centre at Germany's famed Nurburgring.
The car, by the way, managed to lap the famous circuit in 7m 51s, which is indecently fast.
Inside, the treatment is also all about speed.
The seats - recaro-style sports buckets which wrap around you from every angle, are magnificent - among the best seats we've ever settled into and perfect for the huge G-forces this car exerts in corners.
The seats can be adjusted in 16 ways. Yes, 16. So a comfy driving position is easy to find.
The interior is beautifully finished in carbon fibre and sumptuous leather (which, for some reason, Jaguar calls "carbon leather"). There's a very intuitive touch-screen with sat-nav and all manner of adjustments for the cabin, including the imperious Bowers and Wilkins audio system.
There's the now-familiar Jaguar rotary gear selector which rises from the centre console when you press the start button - which pulses like a heartbeat, inviting you to press it. And when you do, it fires up the most extraordinary sound from the big cat's quad exhaust pipes.
One critic described the sounds as like dropping a drum kit down an elevator shaft, which is close.
There's certainly a rattling rawness to this engine, which is a world away from the silken burble of the basic XK - reminiscent of the harsh bark of BMW'S M-Sport engines, or those from Mercedes-AMG.
Which is, of course, the point.
As the revs rise that rattle becomes a symphonic wail - eight pistons and the whine of the supercharger howling in unison - the scenery blurs and things in your rear-vision mirrors become small very quickly indeed.
As in the standard XK, the rear seat is a token gesture.
But even a few minutes folded into the rear was enough to leave one of my teenage children nursing numb feet and a stiff neck.
Putting a set of golf clubs in the rear hatch means removing the longest clubs - the rear seats don't fold forward because of a big beam which runs widthways to stiffen the car's suspension and reduce torque.
If it sounds like I didn't enjoy this car, that would be dead wrong.
It's a magnificent piece of engineering. Sublime. Ridiculous. And whatever comes next.
Above all, powerful.
When you have this much power, it's hard not to be corrupted by it.
See video of the Jaguar XKR-S on a Nurburgring flyer at nzherald.co.nz/driven
