Stuck in Fourth of July traffic from NYC to Boston in a McLaren 675LT, I’ve got too much time to think. What if Paul Revere had a 207-mph, $397,000 supercar for his midnight ride? America’s militiamen would have been on the Concord-and-Lexington case even sooner. That, or the McLaren’s British persuasion would have made Revere switch sides faster than Benedict Arnold. My reverie is broken near Fairfield, Ct., where an impatient young woman in a Lexus sedan cuts the McLaren off in the going-nowhere traffic. A previously unseen cop—I’m thinking a car fan—instantly triggers his rooftop lights, whoops his siren, and pulls the woman and her friends over. Supercar justice served, and I give Ms. Lexus a saccharine smile and a raised thumb as I roll past. I’d been trundling the fireworks-red McLaren over the cratered surfaces of New York, where this radicalized upgrade of the 650S is about as happy as a caged King Kong: huffing, chuffing, dying to break his chains and show who’s boss. Now we’re escaping together, ultimately bound for Monticello Motor Club and a rendezvous with our own Mike Spinelli in his own orange McLaren 570S loaner. That $187,400-to-start 570S, as Spinelli notes, is part of an exploding segment of sub-$200,000 supercars that includes the Mercedes AMG GT, Audi R8, Aston Martin Vantage V12 and the standard-bearing Porsche 911 Turbo S. Looking to make sense of the price-spanning segments, Car and Driver has dubbed these “junior supercars.” Obviously, a buyer’s short pants had still better be stuffed with cash.

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The 570S is itself a cataclysm of speed and corner-hunting prowess, for barely half the price of the 675LT. It looks almost as good as its fraternal twin, ceding advantage only to the 675’s “Long Tail” rear end. That hyper-dramatic view includes the 675’s signature active Air Brake spoiler that helps slow and stabilize the car; a high-mounted pair of titanium exhaust outlets; a sinister diffuser; and larger exit ports to divert superheated air from the mid-engine bay. Both McLarens make otherwise rational people flip the fuck out, including people who have no idea what a McLaren is. In Boston, an adorable little boy, maybe 6 years old, sees the 675LT and launches into a spasmodic Martha Graham dance, flailing arms and jerking airborne as he drags his father toward the car. Yep, it’s Independence Day, and the aliens have landed.

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The 675LT seems made for that boy when he's all grown-up but still craving a pants-wetting emotional overload—comfort and consequence be damned. McLaren uses words like “unique intensity” to describe “the most driver-focused, most exclusive series-production McLaren supercar ever built.” Compared with the lower-case 570S, this 675LT is a capital-S “Supercar,” with a $349,500 base price and a spoken-for production of just 500 copies. An equally limited run of 675LT Spyders has commenced.

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Versus its full-production relative, the 650S, McLaren claims a 40 percent gain in aero downforce, thanks in part to a new carbon-fiber AirBrake that’s enlarged by 50 percent. Industrial-strength side intakes pipe extra air to turbo intercoolers, feeding the 3.8-liter twin-turbo V8 to the tune of 666 horsepower. People who complain about wimpy engine and exhaust notes are directed to this mighty McLaren, which thunders and slobbers like a Tasmanian Devil every time I tickle its throttle. The rush to 60 mph takes 2.9 seconds, but the real fun is just getting started: 124 mph (or 200 kph) arrives in a neck-snapping 7.9 seconds, or the time it takes many cars to reach 60. Credit, in part, an incredible dry-weight claim of just 2,706 pounds—about 800 fewer than a Corvette Stingray Z06. And versus the already loudmouthed 650S, McLaren has stripped out 220 pounds, including sound-deadening carpeting and a windshield that's thinner by 1 mm. On any open battlefield, the whole package makes for a glorious artillery show, including long descents en route to Boston that the McLaren shortens with insane rushes to triple digits. After every eruption, trailing cars rush to catch up, their phone-wielding passengers capturing this rare beast for Facebook feeds and holiday barbecue discussions. The interior is all business, an Alcantara-clad laboratory of speed, yet bare-bones compared with a Ferrari, Lamborghini, or even a decked-out Porsche. That includes McLaren’s obtuse IRIS infotainment system that looks and operates like something re-gifted from Radio Shack. The message is clear: Are you here to check your voice mail and cue up Vivaldi, or to drive? You may notice that the image of a seated driver that's embossed on the climate switches is wearing a racing helmet; he’s the only person this car caters to, including a steering wheel section that at first seems unusually slim but ends up the perfect tactile connection. Ditto for the generous carbon-fiber paddle shifters, which elicit lovely, rat-a-tat changes through the seven-speed, dual-clutch gearbox.

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As I demonstrated across four states, there is no graceful entry into, or exit from, a McLaren 675LT: Duck below its butterfly doors, climb over sills seemingly as tall and wide as Armco barriers, and finally down into optional racing shell seats that seem designed for the limber frames of 15-year-old karters. I had already tweaked my left hip before my drive, and as I write this sentence after five days behind the McLaren’s wheel, the lingering pain finds me in an orthopedist’s lobby waiting for an X-Ray—my regular doctor having refused to sign off on a routine SCCA license physical after seeing me hobble around her office. These chairs string your knees together like chicken thighs ready for the grill, and male occupants will want to monitor their sperm count after extended stretches. By pure coincidence, I just picked up a Car and Driver review in which one writer alleges “permanent hip damage” from the identical racing shells in a 570S. And that guy didn’t drive a far-stiffer McLaren 675LT from New York to Boston, then to the Catskills, then back to Brooklyn immediately after a full day on track. (No, I don’t expect your pity.) Fortunately, owners can opt for standard sport seats like the ones in the 570S, which are almost indescribably more comfortable and accessible, yet still supportive enough for track runs. If public-road logic says the 570S is enough McLaren for anyone, the 3.6 miles of Monticello Motor Club provide the key defense, aside from sheer exclusivity, for the 675LT. Incredibly, it takes the 675LT about two laps to expose the softer underbelly of its little brother. That includes serial turbo lag that leaves the 570S bogging out of slower corners where the 675LT explodes. To stay below the $200,000 mark, the 570S must do without the 675LT’s Airbrake and industry-unique suspension that replaces anti-roll bars with a trick hydraulic system.

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