I have used Syntec on all of my turbo cars for years, no problems. There is a difference between synthetic and mineral oil. The key is thermal management, keeping the oil from exceeding it's limits of survival in extreme temperatures. Mineral oils like temps below 230F. Synthetics survive in temps up to 270F. For an NA car, it may not be as essential, but in turbo cars, it's very beneficial. Synthetics don't acidify like mineral based, and is less likely to coke on turbo bearings.

Do what you want, believe who you want, do the research and you will have the answer.