I did some research into this a while back. 3500 miles is a myth perpetuated by the oil change industry and supported by fifty-year-old science. Back then, 3500 miles was necessary because checmical engineering wasn't what it is today.
A good modern conventional oil will last upward of 7500 miles. A good synthetic will last 10,000 and some will even go 15,000.
That being said, I drive the !@#$ out of my car. I follow Mazda's recommended interval but, with synthetic. Every 7500. I figure that is more than safe.
Semi trucks also have turbos and they don't change their oil nearly that often.
If you're worried, there are companies who sell oil analysis services. You can send them a sample of your old oil and they will tell you things like particulate count, metalic ratios, breakdown, etc.