Hmm i would never buy a demo, when i took a test drive with my salesperson he encouraged me to redline the car as often as I liked. And so I did, and also 100mph+ sprints and spirited cornering. I recommend you look for a car with low millage on the lot or just wait 1-2months for a new ordered car.
Craziest test drive I've had was on a porsche 911 turbo, the salesperson handed the keys to me and my dad and told us to take it for a drive. So we did and got it to 150mph on I 95 a couple of times
, acceleration is incredible in that car keeps pulling like its taking off after 100