Here's clips of decent (for me) laps around VIR in iRacing and in the real world.

And a few notes:

In iRacing the track, car and tires are always in the exact same condition. In real life, the track could be green or rubbered in, or slippery or grippy due to temperature and change in the same day. On top of that, there could be dust or even oil or something else slippery on parts of the track. The cars are matched performance wise pretty closely before each race weekend relative to each other, but not necessarily relative to other weekends and certainly not years ago. The tires could be full treads or more worn down, and I heard different tires are used in the summer series vs. winter (southern) series. All this means comparing lap times is much less meaningful in real life then in iRacing.

For the record though, the iRacing world record in the Skip Barber Formula 2000 car at VIR is just under 2:09 while my best time there is 2:11.8, 2.8 seconds off the world record. The real world lap record is 2:08.5, but the fastest laps of the sessions last weekend were mostly in the 2:13 to 2:14 range. In my best sessions I was about 4.6 seconds off the fastest times of those sessions.

For the track conditions and baseline the cars were tuned to last weekend, the cars seemed to have less grip and longer braking distances then in iRacing. The grip levels in iRacing seem closer to those with the national series tires from the videos I've seen. I also noticed the gear ratios in real car are a bit lower. Second gear comes a bit after 50mph, while in iRacing it comes close to 60mph. I heard the national series tire diameters are different from the regional series. This, in combination with the higher grip levels makes me think maybe the iRacing car is modeled after the national series tire, although the tire has full treads in the graphics like the regional series street tire.

Obviously the real car is more physical to drive, although I wouldn't consider this the main factor holding a sim racer back driving the real car. The G forces in the Skip Barber car are not that great (around 1.5g according to the accelerometer), so extreme neck strength is not required, although you can certainly feel the force. The forces required to turn and hold the steering wheel, press the brake and pull and push the shifter are all significantly higher then any sim setup I've played, although not so much as to require top physical condition to drive. And obviously, most people don't sim race in extreme heat, which can make a significant difference in terms of fatigue.

The brake pedal on cheap pedal sets is obviously not realistic. This makes it hard to practice releasing brake pressure, which is a major key of driving race cars fast, particularly a car like the Skip Barber F2000. The muscle memory of pushing down a pedal that requires much less force and moves more linearly with heavier braking does not help you that much for the real life scenario. Further, if you left foot brake in the sim but not in real life (the steering shaft is in the way on the real car and makes it difficult or impossible to left foot brake with adult sized feet), the technique for coming off the brake in onto the throttle is further irrelevant. I didn't find it hurt me; where the muscle memory I developed playing the sim didn't help at all. I'm thinking about investing in a more expensive brake pedal to practice this more realistically.

The sensation of speed is obviously something that you can only get more comfortable with more real life seat time. The fear of crashing (whether crashing and doing bodily harm or crashing and having to pay for damage) is real and keeps you in check.

I would say the physics of the car are well simulated. The effects of braking and throttle inputs on front to rear weight transfer feel very similar to real life enough so that the sim and real life require similar techniques to drive. I think this is evident comparing the videos. You obviously can't develop the seat of the pants feel though.

As evident in the videos I posted earlier, the draft is huge in the real life skippy car, worth maybe 1-2 seconds a lap at a track like VIR. This means in the real car you can keep up with faster drivers by staying in their draft, pass more easily and adds additional elements of racecraft to the racing.

The track as I mentioned before is in my opinion awesomely recreated. The elevation changes do feel more dramatic in real life.

Do I think iRacing helped me last weekend? Certainly. Can all sim racers expect to be as fast as they are in the sim their first time in a real car? Certainly not.