So long as you're not revving the engine cold I don't see a problem with what you're doing. Nor do I have an issue using "inexpensive" gasoline. My primary reason for using major brands is because I trust the security of their pay at the pump system more than I do those of a convenience store.
The OP said, "...so I would routinely throw them into park in the interstate to test our product..." and "Brake stands and burnouts just to see if it will do it."
You flooring it is nothing like that.
Scott
I will acknowledge that the "throwing it in Park on the highway" might seem extreme...but it isn't. I would only do this in cars that I knew my company supplied the parts for, and I witnessed thousands of hours of tests in labs doing just that, and there had to be ZERO failures (safety critical), so while you might think it was EXTREME, I was replicating something that I had complete faith in.
The other things...brake stands, redlines, burnouts...well a photojournalist does it, and it is in the name of science and reporting. I do it, and I am abusing it...meh. I have done a brake stand in my own car, how else to you measure a good 0-60? If my car is capable, I will do a burnout - I do Auto-X after all, and it is hard to get a good start without it. I had my Buick sideways nearly as much as it was straight on my way to work this morning in the snow, it was a ton of fun.
Driving is a ton of fun, and cars were meant to be driven. They are tested at extreme conditions, and with modern computer control, I would argue it is nearly impossible to abuse them. They won't let the car do something it won't survive.
If a couple brake stands, and a burn-out destroy your car, then it was already on its last legs. It sounds like there are a LOT of folks on here who never experience or appreciate the capabilities of their cars. What a waste of engineering and technology.