As assignments go, this is one of the better ones. Even by Octane standards. Ahead lays 9500ft of unbroken, beautiful runway. And we’ve been given orders to nail it – and see how fast the new 550bhp Jaguar XKR-S will go…

The location’s pretty special too. El Centro Naval Air Force base, located near the California-Mexican border is the home of the Blue Angels formation fliers, boasts an enviable inventory of fighter jets, and was where the film Top Gun was filmed. It’s hard not to let the location, the hardware, the sheer American-ness get to you, especially when the pilot we’ve been talking to tell us that in a drag race, up to 3500-4000ft, the ‘XKR-S will nail an F18’. Cool.

With sense of theatre building, and the radio message telling me to ‘go, go, go’, I nail the throttle – it’s time to see what the big cat will do. Given the huge reserves of torque, there’s no point trying to be clever by disengaging the traction control. I’ve already been given some gold by Jaguar powertrain engineer, Tim Clark: set off in ‘D’, let it change up for you – and then head for sport and the manual paddle shifters.

Nice tip – we’re off with manageable amounts of wheel slip, and nicely balanced traction. Of course, this is not the first thought that comes to mind when presented with this situation. Your senses will be utterly dominated by the soundtrack – one that mixes a Can-Am V8 wail with just enough supercharger whine so remind you of the reason why this 5-litre races for its redline so eagerly. And with the roof down it’s amplified.

Into second, into sport and time to change gears myself. I can barely keep up – a combination of serious g-forces pushing me into the seat, and the odd glance at the speedo to see the big numbers coming up. 0-60 is dispatched in 4.2 seconds – fast, but not mind-bogglingly so, and that’s all down to traction management. 100mph comes up in 8.7 seconds – real supercar pace – and it feels like I’m barely halfway down the strip, when I see 150mph. But ye gads, it’s still pulling, and I mean really pulling, and in a agreeably linear way that big-engined cars do.

I can see the naval officers ahead on the sidelines with chequered flag now – but they’re still a long way away as I glance down and see we’ve hit 170. Does the acceleration feel like it’s tailing off? Slightly, but not much. But the once-smooth surface is starting wake up and has us moving around a little. Still pulling hard, an expansion joint thumps, hard requiring a steering input. At 175mph, And although the XKR-S moves on its adaptive springs and dampers, it still feels nailed.

But the run’s over, and it’s time to brake. And it’s here that the XKR-S impresses yet again, with its big meaty and oh so confidence-inspiring stoppers. Slowing is a whole lot less drama-filled than I was expecting…

But what was the speed? North of 175mph. How far north, we’ll never know, we didn’t have the timing gear out, and I was wide-eyed staring at the view from the windscreen. I didn’t want to miss my braking point, and end up in Mexico, after all.

Of course, a drag-style run up a runway doesn’t tell you nearly enough about any car’s range of dynamic abilities. But what it does prove quite clearly is that Jaguar’s fastest-ever ragtop has genuine, majestic, supercar thrust. And a soundtrack to almost overshadow the sheer theatre and majesty of our surroundings. Once again Jaguar, you’ve done yourself proud. The XKR-S Convertible is a brilliant, charismatic, engaging and beautiful British supercar – that you just happen to be able to take the top off.

And now to the real world

Speaking to Jaguar engineers, one thing that they’re particularly proud of is just how little separates the XKR-S Coupe and the Convertible dynamically. They’ll tell you that it does what it needs to at the Nurburgring Nordschliefe, and can complete the lap in a time that starts with a ‘seven’.

So, seriously capable. It was designed and developed alongside the coupe, and as we end up tackling some of Southern California’s more challenging mountain roads, it’s clear that the convertible does feel very similar to the coupe. That means wonderful throttle response, quick and usable transmission, and delicious turn-in and exit-adjustability.

It also possesses beautifully geared and accurate steering, which is a tad light for press-on drivers, and damping that allows fluid progress on real – pock-marked, cambered and crunchy – roads. That’ll be down to Jaguar’s secret weapon: a testing programme that takes in British B-roads. Brilliant.

The convertible is not completely the same as the coupe dynamically – if anything, it feels even more willing to turn-in than the already pointy coupe. Do we like this slightly surprising development? Yes, once we’re acclimatised. And that’s the whole point of the XKR-S Convertible – it’s a drop-top for hard drivers. But it can waft reasonably effectively too.

As for the rest of the car – it’s standard XK Convertible. So that means a great driving position, slightly scattered ergonomics, a quick folding hood, and a usefully large boot. Likeable it certainly is. The XKR-S Convertible’s aerodynamic addenda is clearly effective, adding downforce, but we wish it was more subtle – and didn’t make it look down in the mouth. As with the coupe, its £20K price premium over the standard XKR will have some customers asking awkward questions – but given the additional performance and subtly enhanced dynamics, it’s great news that enthusiastic drivers are given a genuine choice.

In short, as great as the runway blast was, it was in real-world driving that the XKR-S Convertible’s true range of abilities shone through. Buy with confidence if you want a usable convertible that looks good, drives responsively, sounds joyous, and can work as well on a run to the shops as it does in the mountains.