What is it?Its the new pinnacle of McLarens Sport Series range, the 570Ss harder, sharper, faster cousin\: 96kg lighter, 23 per cent new parts, a car to follow in the footsteps of the fabulous 675LT. Its the McLaren 600LT. Strictly speaking, this is the fourth in McLarens Longtail range after coupe and Spider versions of the 675, and the car that kick-started it all back in 1997, the F1 GTR Longtail. Only nine of those were made. More of these will be made, although McLaren hasnt put a limit on exact numbers, merely saying that production will begin in October this year and all will be built in the next 12 months.In order to maintain the separation between Sport Series (570S et al) and Super Series (720S) models, the 600LT does without movable aero devices and hydraulic cross-linked dampers – those features are still reserved for the (even) more expensive models. Aside from that, just about everything has been seen to. The engine gains new camshafts and a retuned ECU for an extra 30bhp, over 30kg has been removed from the wheels, tyres, brakes and forged aluminium suspension (all important rotational and unsprung weight), the dampers have been recalibrated, the uprights are from the 720S, the track is wider, the ride height lower.Its 74mm longer overall as the front splitter and rear diffuser have both been extended to enhance downforce. Together with the new rear wing, the 600LT develops 100kg of downforce at 248kph. Given the Senna develops 800kg at the same speed, thats not particularly significant. But the 600LT isnt about downforce, its about handling involvement and crispness. And speed, obviously. The headline figures are 100kph in 2.9secs, 198kph in 8.2secs (0.1secs faster than a 911 GT2 RS, 0.6secs slower than a 488 Pista), a 326kph top end and the standing quarter is done and dusted in 10.4secs. All this, and top exit exhausts? Yes, please.What is it like on the road?Key word\: dissection. This is the one thing I took away from the 600LT – the sheer feel, accuracy, precision and control it gives you. In this regard, its even more impressive than the 675LT. Its how the 600LT gets itself into the corner that most impresses. And that starts the moment you hit the brakes. The pedal is reassuringly firm, the bite is huge and the ABS barely intrudes, so it feels like the car has basically snagged an aircraft carriers arrester wire. Theres barely any dive and no differential to get twisted up once you start to turn, so the LT is clean and flat into the corner.It changes direction in a way that defies belief for anything running on modest 225-width tyres. They might be Pirelli Trofeo track day tyres, but I still couldnt get over how much grip they provided. Could they be wider? Maybe, but thats not the point – narrower tyres communicate better, and the 600LT is about communication more than lap time (although McLaren is also keen to point out its faster around a track than the 675LT…). So, you can turn and brake at the same time and know exactly where you are with grip at both ends. If you push it very hard indeed you will get the front end to nudge into understeer, but the McLaren responds so fast you can get that nullified, adjust the balance, correct your line and carry on before youve reached the apex. Seemingly in the space of a few metres, in fact.This is the main thing that differentiates the 600LT to any rival for me. The accuracy and response is such that time seems to slow down during a corner. You have the ability to make corrections many times, to feel how the car reacts and adjust again several times in one corner. Its uncanny. Its akin to a Caterham. At 1356kg its lighter than all its direct rivals, too. Every message is delivered with high-def clarity, every response to steering and brakes is immediate. It gives you the ability to break the corner down into phases, and then sub-divide each one, then pick those apart, to study and feel everything. Its uncanny and absorbing.The engine? Well, alongside the chassis, its the weak link. If you have the revs fully fired up (above 5,000rpm), then lag isnt an issue, but theres no denying the 600LT is more exciting on the way into a corner than on the way out. Yes, the noise is a bit more penetrating thanks to the top exit exhausts, the acceleration maybe a little more urgent, but the tune isnt a belter. So you focus back in on the chassis again, impressed by how it manages traction when it has no mechanical diff, how early you can pick your exit point without the car deviating from its line, how adjustable it is on the throttle.On circuit the 600LT is enthralling. It generates speed without effort and never stops communicating. When you slow down it still has that precision, but Im not sure it has the same breadth of capability as the 675LT. That car was as vivid on road as on track. The 600 copes on road, but is somehow slightly less enthusiastic. Maybe its the engine. Whatever, its a small thing, but it comes across as a little more serious-minded, a little less playful. Get the spec right and itll do distance admirably enough. The glass and carpets might be thinner, but noise isnt an issue and ride quality, while positive, isnt unpleasant. Watch the brakes – when the carbon ceramics are cold, the pedal needs a good shove.The seating position is wonderful, the front scuttle is low, the view out is great. Back the modes off and the gearbox will shuffle up into seventh at little more than 48kph. Should have mentioned it earlier, but the gearbox could occasionally do with snappier downshifts when youre on it. No issues with upshifts though. Bang, bang, bang, home they go, and while the turbo whistles and the exhausts blare, the speed just keeps piling on. A great deal of it.On the insideThe 600LT sets a certain tone inside. Track-focused, unsurprisingly. You sit very low, yet the deep windscreen means the road fast-forwards under your heels. I cant think of a better steering wheel to hold, all the controls are nicely aligned and operate crisply (except those brakes when cold), and Id urge you to stick with the standard seats. Theyre the fixed back chairs from the P1. Trouble is, McLaren also offers the lightweight seats from the Senna, a pair of which saves a whopping 24.6kg. Basically, one piece of carbon with some padding stuck on. Clever stuff, undoubtedly and available in two widths. Ours were the wider ones, and they gave most of us bruised ribs from smacking from side to side. If youre buying a 600LT Im sure McLaren will make sure yours fit properly. Other dubious weight savings are available. Doing without a stereo saves 3.3kg, and if youre into self-basting why not save 12.6kg and junk the AC? Our car benefited from that feature. Dont do it. Youre not that much of a fetishist.VerdictThe most accurate and agile supercar on sale today? I think theres a real argument for that being the case. Where the Ferrari 488 Pista feels almost artificially sharpened with its hyper-sensitive steering, heres a car that picks a corner apart with steely-eyed precision, that exhibits amazing balance and clarity. Does it feel cold-blooded as a result? Maybe a fraction. Its an enthralling car to drive, but at its best when going faster and working harder. Thats when you notice just how impressive it is.People will say it doesnt move the game on as much as McLarens first road-going LT, the 675. And thats true, the 675LT was McLarens break-through car, a step-change from the standard 650S. The trouble for the 600LT is that the 570S is already a terrifically good road and track car. Making progress from that point, while keeping the 600LT within the cost and technological parameters of the Sport Series range so it doesnt tread on the toes of the 720S, is a bigger challenge altogether. Times have changed and expectations are higher. But lets not get bogged down in looking backwards. The 600LT is a crisper, faster and more focused 570S, and a superb supercar in its own right.