"I don't want to wreck any race car, much less somebody else's car," Stewart said. "As a competitor you want to go out and find the limit, but at the same time, you realize that, if you make a mistake, the penalty for that mistake is probably going to be pretty large here.
"It's just amazing how far you can charge the corner. It's easy to see why it's hard for these guys to overtake because it's not a long distance from the time you get off the throttle on the brakes to where you're changing directions. It gives you a much greater appreciation for how hard it is for these guys to overtake each other, what that car's actually capable of."
Hamilton seemed to be having a lot more fun in the stock car. "I just feel like a kid today," he said. "Whilst driving a F1 car is very fun, the competitive side of it is so serious." But by the time he'd finished his laps in a stock car, Hamilton was on the radio to declare "That was fun, man!" and to try out some celebratory burnouts - while his McLaren support crew looked on with concern in case he managed to damage the #14 in the process.
Not that Tony Stewart, the car and team-owner of the #14, was worried. "The part I was worried about he was done by then," he said. "The good thing is, when you see somebody doing a burnout like that, you know they're having a good time. That was kind of the icing on the cake."
The event was held at the New York state road course that hosted the US Grand Prix for 20 years until 1980. "It was definitely good that I got to go out in the F1 car just to kind of get an idea of where the track went," said Hamilton. "The track is absolutely fantastic. It feels like a real classic. It just feels historic when you're driving around. They don't make tracks like that nowadays. When they build new Formula One circuits, they don't build them like this."
The Glen is just a short hop across the Canadian border from last weekend's F1 Grand Prix event in Montreal that included a stunning, dramatic win for Hamilton's team mate Jenson Button - but a less successful experience for Hamilton himself.
"I was feeling the tough weekend this morning," Lewis admitted. "But as the excitement built up, and when I got in the car, and once I got out, I completely forgot about last weekend."
The ride swap exhibition drew an estimated audience of 10,000 along with a lot of excitable motor sports media. The event was organised by Mobil 1, one of Tony Stewart's primary Cup series sponsors and the 'Official Motor Oil of NASCAR', and was a major ambition of Watkins Glen president Michael Printup to bring an F1 car back to the circuit, who admitted: "This was my dream come true."
Watkins Glen hosts one of NASCAR's two road course events in a season of 36 races - the Cup field will be racing there again on August 14, when hopefully the conditions will be rather nicer than the dull and wet weather the car swap faced this week. However, the NASCAR event normally omits the mile-long section of the course dubbed "the boot" and Stewart would like to see that change in the future.
"I enjoyed the long course," Stewart enthused. "I'd never been around it till today. I told [NASCAR competition director] Brett Bodine when we got out of the car after our set-up runs that I would like the opportunity to see us having a shot at running the long course ... I think it would create more passing opportunities, for sure, and it's just such a historic racetrack, and there are some really cool corners down there that we don't get a shot to run on a Cup weekend."